Experimental Biology and Medicine

Continuous dietary administration of rifampin to mice with an established Mycobacterium leprae footpad infection reduced the bacillary solid ratio, with an estimated survival half-life of 5-6 days. In rifampin-treated immunosuppressed animals the survival half-life of solid bacilli, in the absence of host immunity, was 12-13 days. Clofazimine and B1912 produced a significant effect on solid ratio only after a lag period of apparently 100 days. The rate of action was considerably slower than that of rifampin. Intermittent (once monthly) administration of both drugs produced effects similar to those of continuous administration.

Bovine testicular hyaluroni-dase (endo-β-N-acetyl hexosaminidase) has a significant corrective effect on cultured Hurler fibroblasts. Nonspecificity of this effect is indicated by its equally strong corrective effect on Hunter fibroblasts. Although all specimens of hyaluronidase also possessed iduronidase activity, a separate corrective effect could be attributed to the endo-N-acetyl hexosaminidase activity of at least one hyaluronidase (Wyeth M-151) for four reasons: (i) its very low content of iduronidase activity; (ii) a decrease in intracel-lular macromolecular mucopolysaccharides (believed to be largely dermatan sulfate) with a corresponding increase in intracellu-lar and extracellular oligosaccharides; (iii) no measurable increase in iduronidase activity of hyaluronidase-treated cells despite near maximal correction; (iv) direct correlation between Hurler cell correction and hyaluronidase activity when enzymes of different strength were used at less than maximal correction.

In summary, the present study is further evidence for an interaction of angiotensin with adrenergic neurons in the myocardium. Concentrations of the peptides which do not display inotropic activity in point-stimulated atria result in marked facilitation of the release of neurotransmitter and DβH from adrenergic neurons in field-stimulated atrial preparations. The neuronal receptor for angiotensin is relatively resistant to blockade with an angiotensin antagonist, saralasin.

The incubation fluid from 24-hr cultures of normal guinea pig small intestines was found to contain activity capable of inhibiting the migration of normal guinea pig peritoneal macrophages. Each of three different culture fluids showed macrophage inhibitory activity in the 25,000-55,000 mol wt range when subjected to Sephadex G-100 gel filtration. One of these three preparations also contained inhibitory activity in the excluded volume.

The low molecular weight activity was nondialyzable and heat stable to 56° for 30 min. It was destroyed by boiling for 1 hr, and its activity was reversed by 10^-4 M epi-nephrine. Based upon these properties it is suggested that this activity was due to migration inhibitory factor (MIF). The high molecular weight inhibitor was stable to heating and its activity was not reversed by epi-nephrine. This material was most likely endotoxin. The presence of MIF, which may be associated with T-cell activity in the intestine, suggests that cell-mediated immunity (CMI) could play a role in local protection against gut infections. Furthermore, its presence in normal intestinal secretions suggests that some MIF-producing cells are always being stimulated by normal flora. The question is thus raised whether further specific stimulation of local CMI in the gut could be successful.

Isoproterenol infusions depress pentagastrin (PG)-stimulated secretion of acid and pepsin from both gastric fistulae and denervated (Heidenhain) pouches in conscious dogs. It was not found to do so if methacholine replaced gastrin. Propranolol reversed the isoproterenol depression of PG stimulation but had no effect on isoproterenol plus methacholine except on the fistula where both acid and pepsin were depressed. It is felt that PG and methacholine act by differing mechanisms both on chief and parietal cells.

The effect of melatonin on the LH-release response after the administration of synthetic LH-RH and clomiphene citrate was investigated in adult male rats. The sc administration of melatonin (1 mg/ day) for 6 days produced a significant decrease in serum LH levels and in seminal vesicles and ventral prostate weights. On the other hand, the daily injection of 0.01 mg/100 g of body weight of clomiphene citrate during 6 days significantly stimulated LH levels and the weights of the accessory sex glands. Simultaneous treatment with melatonin and clomiphene produced an inhibitory effect similar to that obtained with melatonin alone. Neither pretreatment with melatonin (1 mg/day, sc for 6 days) nor its simultaneous iv administration (500 μg) with 75 ng of LH-RH modified the LH-release in response to the hypothalamic hormone. The fact that melatonin was able to suppress the effect of clomiphene, which is probably exerted at the hypothalamic level, but not the action of LH-RH on the pituitary, appears to indicate that the hypothala-mus may be the site involved in the inhibitory effect of the pineal principle on the reproductive function.

Lipolytic activity measured at pH 8.6 in bovine corpora lutea exhibited classical properties of lipoprotein lipase (LPL) in terms of serum and heparin stimulation and NaCl inhibition. LPL activity was measured in 23 corpora lutea collected at different stages of the estrous cycle and early pregnancy. The LPL activity in cyclic corpora lutea (μmole FA released/hr/100 mg acetone powder) was low at Days 4-8 of the estrous cycle (3.1 ± 1.5: mean ± SE) and at Days 19-20 (1.6 ± 0.6). However, high activity of the enzyme was found at Days 12-15 of the cycle (11.8 ± 1.8); these concentrations were significantly (P < 0.01) elevated over those found at Days 4-8 and 19-20. The enzyme activity began to decline at Days 16-18 of the estrous cycle (5.1 ± 1.7). Low enzyme activity was found in the corpora lutea removed from two cows at Day 22 of pregnancy.

Progesterone concentrations were measured in 16 of the 23 corpora lutea and a good correlation (r = 0.75, P < 0.01) was found between lipoprotein lipase and progesterone concentrations of the tissue. The data suggest that LPL may be involved in controlling the transfer of fatty acids, including arachidonic, from plasma lipopro-teins to luteal tissue.

The muscular dystrophies caused by dy and dy ^2J on a C57BL/6J genetic background are similar in quality. At 1 month, slight differences occur in distribution of the muscle lesions, diffuse and focal, respectively, but at 3 months little, if any, differences exist. The dy dystrophy appears the same histologically on either the C57BL/6J or original 129/ReJ and 129B6F₁ backgrounds.

Sex and strain differences in survival were studied in 7-9 month old germfree mice following transfer to a conventional colony. One outbred and three inbred strains were observed. All outbred CD-1 mice survived transfer and in 4 months increased their weight by 50%. The majority of inbred mice survived 7 months after transfer. Sex differences in survival were evident throughout the experimental period and were most marked 7 months after transfer. An unexpected new finding was the viability of the male sex in germfree mice after transfer. Possible explanations are considered.

Hypertonic mannitol previously has been shown to improve cardiac function, increase collateral flow, and decrease epicardial ST segment elevation following coronary occlusion in anesthetized or awake dogs. The present study quantitates by morphologic techniques, the effect of hypertonic mannitol on infarct size. Ischemic injury was produced by proximal occlusion of the circumflex artery for 40 min and necrosis was assessed after 48 hr of reflow. One group of dogs was given isotonic saline and the other hypertonic mannitol beginning the infusions just prior to, during, and for a short period after the release of the circumflex coronary artery occlusion. Serum osmolality increased by approximately 40 mOsm in the mannitol group. The administration of hypertonic mannitol was associated with a 40-50% reduction in infarct size measured histologically. The incidence of ventricular fibrillation during occlusion and following release of the circumflex coronary artery occlusion was greater in mannitol-treated dogs although the difference was not statistically significant. Thus, the data obtained in this study extend previous observations and provide direct evidence that hypertonic mannitol can reduce infarct size in dogs with temporary circumflex artery occlusion and reflow.

The virus-cell relationship of RS virus and the HEp-2 cell line has been examined. The production of cytopathic effect (c.p.e.) on HEp-2 cells has been found to be dependent upon the passage level of the cell line. Cells at lower passage levels exhibit c.p.e. in the form of syncytium formation, while those at higher passage levels no longer exhibit this effect. Cells infected at higher passage levels are covertly infected and continue to produce large amounts of infectious virus which remains cell-associated. On continued passage, these cells remain infected with virus but show no c.p.e. and release little if any infectious virus into the medium.

Examination of the RNA species present in infected cells revealed that similar species are present in both the overtly and covertly infected cells.

Adrenal 5α-reductase activity was measured in female rats 0, 2, 5, and 6 days after hypophysectomy. Enzyme activity increased progressively exhibiting a 35-fold elevation at 6 days. The effects of high (250 μg/100 g of body wt), intermediate (25 μg/ 100 g of body wt), and low (2.5 μg/100 g of body wt) daily doses of bovine prolactin and bovine growth hormone were compared at 2 and 5 days posthypophysectomy. At 2 days, enzyme activity was partially inhibited by the high and intermediate doses of prolactin and not affected by growth hormone. At 5 days all doses of prolactin were inhibitory, whereas enzyme activity was suppressed only by the high dose of growth hormone. With a given dose of hormone, the amount of suppression of enzyme activity is greater at 5 days than at 2 days posthypophysectomy. In 5-day hypophysectomized rats the inhibitory effects of prolactin and growth hormone were additive. It is concluded that: (i) hormonal sensitivity and responsiveness of the adrenal reductase pathway increases with duration of pituitary ablation; (ii) the reductase pathway is more sensitive to the effects of prolactin than growth hormone; and (iii) the effects of growth hormone and prolactin on reductase activity are mediated via different mechanisms, as suggested by the additive effects of individual hormones.

Highly purified hepatitis B virus surface antigen (Australia antigen) purified by physical and chemical procedures from infected human plasma was used to prepare hepatitis B vaccine. The purified antigen was treated with formalin and the vaccine was tested exhaustively for safety by ordinary procedures and additionally in marmosets (for live hepatitis A virus) and in chimpanzees (for live hepatitis B virus). The vaccine was highly potent, inducing antibody in guinea pigs, grivet monkeys, and chimpanzees given three doses of vaccine containing up to 20 μg of hepatitis B antigen per dose. A protective efficacy trial was carried out in chimpanzees that were given three doses of vaccine subcutaneously and then challenged intravenously with 1000 chimpanzee infectious doses of human hepatitis B virus. All of five unvaccinated control animals developed hepatitis B virus an-tigenemia following challenge and all of six vaccinated animals were protected, including one animal that had failed to develop detectable antibody following vaccination.

(i) Omission of L-methionine from the medium resulted in an 80% population reduction. Substitution of D, L-homo-cysteine corrected methionine deficiency in C. briggsae in the presence of supraoptimal vitamin B₁₂ and folic aid.

(ii) An absolute vitamin B₁₂ requirement in C. briggsae developed in the medium containing homocysteine at the second subculture. Concentration of 6 ng/ml of vitamin B₁₂ (at 100 ng/ml of folic acid) was sufficient to support maximum growth of C. briggsae in the medium containing homocysteine.

(iii) It was found that either supraoptimai folic acid (2000 ng/ml) or supraoptimal vitamin B₁₂ (3750 ng/ml), with homocysteine, supported very little population growth of C. briggsae. However, supraoptimal folic acid and supraoptimal vitamin B₁₂ together supported a maximum population growth. Therefore, it was concluded that both vitamin B₁₂ and folic acid were required for the biosynthesis of methionine from homo-cysteine. Studies also showed that the two vitamins spared each other for population growth in the medium containing homocys-teine.

This study has demonstrated high correlation between the radiometric and spectrophotometric determinations of gastric mucosal aminopyrine clearance. The radiometric method is technically easier, allows a larger number of samples to be determined and is safer to the subject. The clearance of small amounts of [¹⁴C]aminopyrine was unaffected by large doses of unlabeled aminopyrine showing that mucosal extraction is not concentration limited. Small amounts of [¹⁴C]aminopyrine may provide an excellent tool for examining the role of mucosal blood flow in the pathogenesis of gastric disease in man.

Cortisol-sensitive and cortisol-resistant lymphoma PI798 cells specifically bind [¹²⁵I]insulin. Resistant lymphocytes bind 40% less insulin than sensitive cells. These results suggest that insulin (or insulin-like substances) may play a role in growth regulation and/or response of this tumor to glucocorticoid therapy.

Levamisole has been shown to augment the in vitro responsiveness of lymphocytes to PHA stimulation. The response of lymphocytes of 14 (42%) of 33 patients with pulmonary tuberculosis was augmented by levamisole. Augmentation was observed in 9 (64%) of 14 PHA hyporesponsives lymphocytes and in 5 (26%) of 19 normo-responsive lymphocytes.

Penicillin pretreatment enhanced the rate of PAH uptake into separated proximal tubules (collagenase digestion) from 2-week New Zealand white rabbits. A double reciprocal plot of these data suggests that penicillin increases the maximal velocity of PAH uptake. Na, K-ATPase was less in adult tissue but was unaffected by penicillin. No ultrastructural changes could be attributed to the treatment. Thus, substrate stimulation of PAH transport does not involve Na, K-ATPase and probably involves soluble, rather than structural proteins.

Peripheral plasma progester-one concentrations were measured in New Zealand rabbits every 6 hr beginning 12 hr before and continuing until 96 hr after either natural mating, hCG injection, or saline injection. The number of ovulation points in naturally mated animals (9.3 ± 0.6, mean ± SE) was not significantly different from that in hCG-injected animals (8.6 ± 1.5). There was a surge in progesterone secretion following both mating and hCG injection. Plasma progesterone concentrations reached a peak prior to ovulation and then fell to basal levels at the time of ovulation. Beginning at approximately 30 hr after the ovulation-inducing stimulus, there was a progressive, significant (P < 0.001) increase in plasma progesterone concentration, which continued for the duration of the sampling period. The initiation of the postovulatory increase in progesterone secretion corresponds temporally with the movement of eggs from the ampullary-isthmic junction into the isthmus. The progressive increase in plasma progesterone between 30 and 72 hr after the induction of ovulation corresponds with the gradual movement of eggs through the isthmus into the uterus. The data suggest that movement of eggs through the oviductal isthmus is influenced by the postovulatory secretion of progesterone.

The effect of detergent treatment of the canine gastric mucosa on transport of drugs from blood to gastric juice was studied using a chamber technique, in vivo. Detergent treatment was found to increase antipyrine and aminopyrine transport. Facilitation of drug transport was associated with disruption of the gastric mucosal barrier and an increase of aminopyrine clearance.

Gentamicin nephrotoxicity was examined in rats on normal, high, and low sodium diets. Low sodium diet markedly potentiated nephrotoxic effects of the drug as evidenced by animal mortality, renal failure, pathological changes, and increased renal cortical concentration of the drug. High sodium intake reduced the cortical concentration of gentamicin but renal function and ultrastructure were similar to normally fed rats given in the same dose.

Pituitary prolactin (PRL) content was reported to be decreased in hypothyroid animals (1, 2). Serum levels of PRL as measured by radioimmunoassay were observed to be unchanged by hypothyroidism in rats and human subjects (3, 4). Recently, the response of PRL secretion to thyrotrophin-releasing hormone (TRH) was shown to be higher in hypothyroid than in euthyroid animals, and the stimulating action of TRH on prolactin release was abolished by treatment with thyroid hormones (4, 5). Onishi et al. (6) reported that PRL release in response to TRH and to chlorpromazine (CPZ) was eliminated in hyperthyroid humans. The precursor of 5-hydroxytryptamine (5-HT), 5-hydroxytryptophan (5-HTP), and CPZ, an adrenergic receptor blocker, both have been observed to greatly increase PRL secretion (7-9), perhaps by decreasing prolactin release-inhibiting factor (PIF) or by increasing prolactin releasing factor (PRF) in the hypothalamus (9).

Materials and methods. Mature male Sprague-Dawley rats weighing 200-225 g were obtained from Spartan Research Animals (Haslett, Mich.). The rats were housed in a light-(14 hr light and 10 hr darkness daily) and temperature-controlled (26 ± 1°) room, and Received Wayne Lab Blox rat pellets (Allied Mills, Chicago, Ill.) and tap water ad libitum.

The rats were grouped as follows: (1) intact controls, (2) thyro-parathyroidectomized (THX), (3) THX and 2.5 μg thyroxine (T₄) per 100 g body wt, (4) THX and 10 pg T₄ per 100 b body wt. All surgically treated rats were given 0.2 ml Longicil (Fort Dodge Laboratories, Inc., Fort Dodge, Iowa), an antibiotic, by im injection to avoid infection. The sodium salt of L-T₄ (Nutritional Biochemical Co .) was dissolved in slightly alkaline saline (pH 8.0) and given sc to groups of three and four rats once daily. Rats in the intact control and THX groups were injected with alkaline saline (pH 8.0) only. After operation, the THX rats were given 1% calcium lactate solution instead of tap water to prevent tetany.

The frequency and magnitude of serum antibody response to type A and B influenza viruses induced by whole virion and subvirion vaccines were essentially comparable . Immunization was followed in vaccinated individuals by an antihemagglutinin antibody response to the common antigenic determinant shared by the type A H3N2 viruses. Relatively few individuals developed antibody to the type-specific determinant.

In the mammary glands of mice, levels of cyclic AMP increased during pregnancy and then fell precipitously following parturition. In contrast, levels of cyclic GMP fell during the gestation period and then rose rapidly during the early days of lactation. Adenylate cyclase and cyclic AMP phosphodiesterase activities were elevated during the pregnancy and lactation periods.

The divalent cation chelators, CaEDTA and EGTA, were demonstrated to exert opposite effects on contractions of rat aortic smooth muscle induced by withdrawal of external magnesium ([Mg²⁺]_o). Addition of CaEDTA potentiated such contractions more than 100%, while EGTA promoted rapid relaxation. Rapid relaxation of contractions induced by withdrawal of [Mg²⁺]_o could also be induced by Mn, Ni, and Cd but not Sr. Using EC50's, a relative descending order of contractile inhibition was noted for the divalent cations: Mn > Cd > Mg > Ni. The ability of CaEDTA to potentiate contractions produced by withdrawal of [Mg²⁺]_o, as well as the ability of divalent cations to relax contractions of aortic smooth muscle, appears to be related to actions on the transmembrane flux of Ca²⁺. These findings thus lend support to the view that Mg ions either play an important role in regulating membrane permeability to [Ca²⁺]_o or occupy membrane sites which are exchangeable with membrane-bound Ca in certain types of arterial smooth muscle.

Canine respiratory cells, obtained by bronchial lavage, and blood leukocytes were monitored to observe cellular changes following acute and chronic immu-nosuppression. Irradiation (350 R) produced bone marrow suppression and prompt peripheral blood leukopenia, but did not affect recovery of pulmonary alveolar macrophages or lymphocytes for 12 days after. Treatment for 6 weeks with daily methylprednisolone (1 mg/kg) caused a progressive decrease in the number of recoverable respiratory lymphocytes, whereas alternate day methylprednisolone (2 mg/kg) had less effect. Cyclophosphamide in combination with steroids generally augmented the progressive loss of blood and respiratory lymphocytes. Recovery of alveolar macrophages was not changed appreciably. Thus, the population of lung macrophages, sampled by pulmonary lavage, withstood acute and chronic forms of immunosuppression very well. In contrast, canine lymphocytes seem more susceptible to injury, especially to drug regimens containing steroids.

A serologic test for measurement of antibody to V-Z virus by immune adherence hemagglutination is described. Initial evaluation of the test has shown it to be highly sensitive, specific, rapid, and simple to perform. The V-Z antigen may be stored at −70°, and the test could be performed in any routine serology laboratory.

Lymphocytes obtained from rat spleens were sensitized in vitro to sheep erythrocytes. The sensitized lymphocytes did not synthesize antibody but when injected into unimmunized rats did stimulate antibody production to sheep erythrocytes. Analysis of the location of 7 and 19 S plaque-forming cells in the recipient rats indicated that these two antibody synthesizing cell populations arise from different lymphocytes. It was also found that the sensitized lymphocytes could react only with a limited number of antibody synthesizing cells.

Both excess dietary vitamin E and vitamin E deficiency in rats can significantly depress the activity of GSH peroxi-dase in liver and plasma of rats. Of all the six levels of vitamin E tested in this study, the dietary level of vitamin E found to maintain the maximum activity of GSH peroxi-dase in tissues of rats was somewhere between 25 and 250 IU/kg diet. This study conclusively indicates that the excess dietary vitamin E represses GSH peroxidase activity.

Blood was drawn from the portal vein of rats immediately after the insertion of ⁶⁵Zn into the duodenal lumen. Analysis of the plasma from the portal blood demonstrated that the major portion of absorbed ⁶⁵Zn was bound to transferrin. When apotransferrin was incubated with ⁶⁵Zn-la-beled basolateral plasma membranes, 60% of the isotope was removed from the membrane . Zinc-free albumin prepared with his-tidine removed 25% of the ⁶⁵Zn from labeled membranes and histidine had no effect. These results demonstrate that transferrin functions in the absorption and transport of zinc.

The jejunal mucosal membrane of albino mice was used to study the electrical properties and ion transport. The membrane was bathed in Krebs-Ringer solution with or without glucose. When ethac-rynic acid (EA), furosemide, or amiloride was added to the bathing fluid of both sides, a transient increase followed by a decrease of both potential difference (PD) and short circuit current (I_sc) were observed. In glucose-containing bathing medium, EA inhibited both net Na and Cl flux and residual flux; however, EA had little effect on both Na and Cl flux in glucose-free bathing medium. Studies using everted intestinal sac technique showed that EA inhibited both glucose and L-tyrosine across the mucosal membrane against concentration gradients. Furosemide and amiloride were less potent than EA in inhibiting the Na and Cl flux when the bathing solution contained glucose. But these two compounds had no effect on glucose and L-tyrosine transport across the intestinal mucosa. Furthermore, they did inhibit Cl flux even in the condition of glucose-free bathing medium. It is postulated that all three diuretics act on the brush-border membrane of the intestine. EA probably inhibits the Na-glucose co-transporting system; furosemide and amiloride inhibit the simple diffusion process of Na entry or Cl exit by decreasing the conductance of the membrane.

Antral and serum gastrin concentrations were found to be significantly lower in female than in male rats. Following ovariectomy, serum gastrin concentration significantly increased to male levels; tissue gastrin also increased, but not significantly. Daily injections of estradiol benzoate (2 μg/ day) abolished the rise in gastrin levels after ovariectomy. Antral and serum gastrin concentrations were significantly higher in lac-tating rats than in any other group tested. The possible relationships among sex-dependent changes in food intake, gastrin concentration, and gastric secretion are discussed.

Rat liver hepatoma cells in monolayer tissue cultures were exposed to various concentrations of ether (E), isoflur-ane (IF), halothane (H), or methoxyflurane (MF) for 5 hr. Loss of intracellular enzymes into surrounding media was used to quanti-tate cytotoxic effects. Drug concentrations in cells and media were monitored during some of the experiments. Dose- and concentration-related cytotoxic effects were evident for all drugs. The order of cytotoxic potency was MF > H > IF > E. The differences were not related to the intracellular concentrations accomplished by each drug. The direct dose-related toxic effects of MF and H on the cell membranes suggest that other than hypersensitivity factors may play a role in the hepatotoxicity from these halo-genated anesthetics. The correlation between the in vitro effects on liver cells and the suggested comparative hepatotoxic potentials of these drugs in man supports the possible usefulness of this method to gather additional information on comparative hepatotoxic potential of general anesthetics.

High capillary density and small muscle fiber diameters were found in the sternothyroid muscle of dogs native to 4350 m. The number of capillaries per square millimeter was three times greater while the diameter was less than half of those obtained in the same muscle of nor-moxic dogs. These findings suggest that tis-sular adaptative mechanisms are important in the process of acclimatization to hypoxia, contributing to the maintenance of adequate levels of Po ₂ in the tissue in the presence of hypoxemia.

The adult heart rate responds to stimulation of the sympathetic and parasympathetic nervous system. These responses are mediated by the release of norepinephrine and acetylcholine (ACh) which act on beta-adre-nergic and on muscarinic-cholinergic receptors, respectively. During rat embryogene-sis, the heart commences to beat during Day 10 and circulation is established before these nerves reach and innervate the heart on Day 15 (1-3). The effect of ACh on the beat rate of excised rat embryo hearts has been reported by two groups of workers and their conclusions differed; Hall (4) observed a decrease in rate in the Day 11 ½ and older embryos but Pager et al. (5) could not demonstrate this effect until Day 16½. Our studies using the whole explanted embryo suggest an explanation for this discrepancy.

Cholinergic receptors can be experimentally distinguished into two types by (a) their response to atropine, which selectively blocks muscarinic receptors, and (b) to curare, which selectively blocks nicotinic receptors. The experiments reported in this paper demonstrate the presence of cholinergic receptors in the preinnervated intact embryonic heart, consistent with Hall's result in the excised heart, classify them as being of the muscarinic type and show that they are independent of the adrenergic receptors in their action and time of functional appearance. We have found (6) in the explanted whole embryo that the adrenergic response of the heart appears during Day 10 concom-mitant with the onset of heart function, a result similar to that of Hall's with excised hearts. Our findings indicate that cholinergic response first appears approximately ½ day later in development than the adrenergic response, a finding also first observed by Hall.

Methods. Embryos were explanted at either Day 10 1/2 (10–15 somites) or Day 11 (21-26 somites) of gestation. The explantation procedure followed was as described in New (7), Shepard et al. (8), and Robkin et al. (9).

Guinea pigs inoculated with virulent Rickettsia rickettsii responded with a significant increase in plasma copper concentration within 1 day, preceding fever and detectable rickettsemia by 2 and 4 days, respectively. A decrease in serum zinc concentration coinciding with peak rickettsemia was detectable on Day 5. Evidence of altered host nitrogen metabolism during this illness included a doubling of plasma sero-mucoid concentration and a significant rise in the plasma phenylalanine/tyrosine ratio.

Mouse embryos in the pronu-clear zygote stage were either irradiated in utero with a dose of 15 rad of fast neutrons or were sham-irradiated. Those animals that survived at least 30 days after birth were observed until their natural death. We investigated the percentage incidence and mean age at death for each of the principal neoplastic diseases seen on postmortem examination and also cumulative mortality distributions. No statistically significant differences were found between irradiated and sham-irradiated mice of the same sex.

Effects of iv and ia administration of histamine and its H₁ and H₂ blockers (diphenhydramine and metiamide) on systemic arterial pressure, heart rate, and uterine and iliac blood flows were investigated in unanesthetized, chronically instrumented nonpregnant ewes.

Intravenous histamine produced tachycardia, hypotension, and decreased iliac and uterine blood flows. In contrast, ia injections produced a significant increase in blood flows in these vascular beds which was dose-dependent.

Evidence is presented to show that some of the circulatory actions of histamine may be related to stimulation of H₁ while others may be related to H₂ receptors. The peripheral circulatory action produced by iv histamine is probably secondary to its effects on reducing cardiac output. The uterine and iliac vascular beds contain mostly H₁ receptors since their response to histamine can be blocked almost totally by Benadryl and not by H₂ antagonist metiamide.