Experimental Biology and Medicine

Sprague Dawley rats were adrenalectomized (Adx) and then eviscerated (Evs) 4 days later. Various surgical procedures were used during the evisceration to preserve or eliminate liver and/or kidney function. Non-Adx Evs rats were used as controls for each group. Abdominal aortic blood was used to measure: blood glucose (BG), urea nitrogen (BUN) and ketone bodies (KB) as well as plasma free fatty acids (FFA) and amino nitrogen (AN), 3-72 hr after evisceration. All eviscerated rats lack insulin and with the liver in situ can maintain a hyperglycemia if the adrenals are present. Adx Evs rats do not develop this diabetic pattern. Furthermore, non Adx rats without a functional liver can sustain 80% of normal BG if the kidneys are in situ but Adx Evs rats require the liver as well. In the abence of the kidneys, protein metabolites are accumulated in the blood in both Adx and non Adx Evs animals.

FFA elevations occur in the Adx-Evs animal but are markedly lower than in the non-Adx preparation. The absence of insulin partially overrides the effect of Adx on this parameter.

Radioimmunoassays specific for rat serum albumin and rat α-fetoprotein have been described. These systems are capable of measuring the serum proteins in as little as one nanoliter of rat serum. Negligible cross reaction with other albumins and globulins was observed in sera from a variety of animal species. These radioimmunoassay systems have proved most useful in the quantitation of RSA and AFP in extracts from tissues where their mass and their affinities for estradiol could interfere with the estrogen receptor and hence compromise analyses of the binding events in estrogen action studies. Such interference would be amplified in the less mature rat, be influenced by the method of tissue preparation, and most likely occur in tissues characterized by femto and subfem-tomolar levels of estrogen receptor.

The purpose of this study was to determine the extent of involvement of the inorganic phosphate ion (Pi) in exercise hyperemia. Lymph and venous plasma from resting and contracting muscles of the canine and feline hindlimbs were analyzed for Pi. The vasoactivity of exogenous inorganic phosphate was assessed by close intra-arterial infusion of the sodium monobasic phosphate while blood flow and lymph and venous plasma Pi concentrations were determined. The results showed that there was no increase in venous plasma Pi with muscle contraction, only a small increase in lymph Pi, and that the phosphate ion is very vasoinactive. We therefore conclude that the inorganic phosphate ion may play only a minor role, if any, in active hyperemia in skeletal muscle.

Female rats with carcinogen-induced mammary adenocarcinomas were injected 2-3 times daily with naloxone or naltrexone, specific antagonists of endogenous opioid peptides. Both drugs completely prevented mammary tumor growth without inducing regression of the cancers, effects believed to be due to reduced prolactin and perhaps GH secretion. These results suggest a possible role for endogenous opioid peptides in rat mammary tumor growth.

Thirty-five mg of the LH-RH antagonist (D-Phe⁶, D-Trp³, D-Phe⁶)-LH-RH inhibited the LH response of chimpanzees given 10 μg of LH-RH to 33% of the amount released by control animals. Seven mg of the same analog also attenuated the LH response, but the inhibition was not statistically significant. Neither dose level of the inhibitor significantly altered basal gonadotropin levels. These data indicate that LH-RH antagonists have at least an acute ability to diminish the response to exogenous releasing hormones without acutely affecting basal gonadotropin secretion. They further suggest that a non-human primate model may be used to test the efficacy of these compounds as potential contraceptive agents.

In dogs with electrodes chronically implanted on the stomach and duodenum, graded doses of intravenously infused synthetic human unsulfated little gastrin (G17-I) produced, in both the stomach and duodenum, graded increases in a) frequency of pacesetter potential, and b) incidence of pacesetter potentials with action potentials. The threshold doses of gastrin for these effects were about 25 pmol kg^-1 h^-1 in the stomach and about 50 pmol kg^-1 h^-1 in the duodenum. These doses of gastrin are similar to the threshold dose for gastric acid secretion.

The effect of GABA on prolactin secretion from the pituitary under physiological conditions in lactating female rats and in normal male rats was investigated. Prolactin was measured by RIA in blood samples taken from lactating mothers by means of an intrajugular silastic catheter, 10-15 days after delivery. GABA in doses of 825 μg, but not 150 μg, microinjected into the third ventricle partially suppressed the serum prolactin rise due to suckling. Aminooxyacetic acid (AOAA), 30 mg/kg ip, which has been reported to produce a sharp increase in GABA content in the CNS, significantly suppressed the prolactin increment during the suckling period. By contrast, in non suckled mothers, GABA or AOAA was ineffective in altering serum prolactin. In normal male rats, GABA and AOAA were able to partially suppress prolactin release due to ether stress. These results clearly show that increments in GABA content in the brain after microinjection of exogenous GABA or following suppression of enzymatic inactivation of the endogenous amino acid were able to inhibit prolactin release under physiological conditions.

Male Sprague-Dawley derived rats fed a moderately high sodium diet became hypertensive by the 6th dietary month. After the 12th dietary month, the urinary excretion of epinephrine and norepinephrine was moderately increased in this group. The inclusion of a small dietary supplement of potassium in the diet had an ameliorating effect upon the development of hypertension and resulted in lower excretion rate for catecholamines.

Neither milking nor changes in ambient temperature affected TSH concentrations in serum of cattle. On the other hand, serum PRL concentration increased 10-fold after milking and was positively correlated with ambient temperature. These results do not support the premise that endogenous TRH releases both TSH and PRL in cattle.

Intravenous infusion of [1-Deaminopenicillamine, 4-valine, 8-D-arginine]-vasopressin (dPVDAVP) inhibited the mesenteric vasoconstrictor response to arginine vasopressin in cats but the compound initiated little or no vasodilatation when administered alone in hypophysectomized cats and it failed to inhibit the mesenteric vasoconstrictor response to angiotensin II. The results are consistent with the interpretation that dPVDAVP is an antagonist of the vasoconstrictor activity of arginine vasopressin.

The major component, 2,2′,4,4′,5,5′-hexabromobiphenyl (HBB-4) of the polybrominated biphenyl fireMaster FF-1, involved in the contamination problem in Michigan, did not produce either an edema in embryos and newly-hatched chicks or a decline in hatchability when fed to laying chickens. However, fireMaster FF-1, containing an equivalent level of the HBB-4 isomer caused the expected deleterious effects.

Hypophysial isografts stimulated mammary HAN formation and tumorigenesis in MTV-expressed female mice, even when the grafts were removed at 21-23 days of age. Exposure to the grafts (presumably secreting prolactin) during shortterm postnatal periods may induce proliferation of mammary tissue and result in early onset of mammary tumorigenesis, either directly or through the animal's endocrine system. This exposure also results in increased occurrence of uterine cyst formation in SHN mice.

Direct pressure measurements were obtained simultaneously in the aorta, right atrium, pulmonary artery and left atrium on anesthetized, open-chest rats on a respirator. Mean pressures in the aorta were 105, right atrium 3.3, pulmonary artery 16, and left atrium 5.8 mmHg. The aortic pressure is comparable to previously published values. These vascular pressures should provide helpful guidelines to those investigators utilizing the rat in experimental physiological studies.

Obstruction and reestablishment of coronary artery flow both markedly lower the threshold for ventricular fibrillation (VF). This reduction in threshold is partially reversed by infusion of Prenylamine, a drug with slow channel blocking and coronary artery vasodilating properties. Mean blood pressure and heart rate were unaltered. Prenylamine administration also elevated the VF threshold in the nonischemic myocardium. Its effect on reperfusion VF threshold is unique, since commonly used antiarrhythmic drugs exert no such effect.

A cell line derived from a murine teratocarcinoma was cultured in growth medium supplemented with either 10% or 1% fetal bovine serum or was grown in chemically-defined medium buffered with either a combination of HEPES and sodium bicarbonate or with bicarbonate alone. The sugar content of a particular glycoprotein secreted by these cells was markedly different in each case. No differences were noted in antigenicity or amino acid composition, including amino and carboxyl terminal amino acids. Differences in molecular weight were attributable to the difference in carbohydrate content. These data indicate that the level of glycosylation of proteins in vitro is dependent on the medium composition, including apparently unsuspected components such as buffers.

5α-pregnane-3α,20α-DIOL (5α-DIOL), a steroid which is secreted by the rat ovary and which may be formed from progesterone and 20α-hydroxyprogesterone in the brain and in the anterior pituitary, stimulates LH release while inhibiting FSH secretion in ovariectomized estrogen-primed rats. The steroid does not influence gonadotropin secretion when given to castrated female rats in the absence of exogenous estrogens. These data suggest that the process of 5α-reduction plays a role in the induction of the “positive” but not of the “negative” feedback activity of progestogens.

Segments of the jejunum and ileum of 14-15-day-old and 42-day-old rats were perfused in situ with isotonic or hypertonic calcium free solutions. There was net secretion of calcium in all segments perfused. Rates of net secretion of calcium were several fold and significantly greater in segments of the 14- to 15-day-old than in corresponding segments of the 42-day-old rats. In the 14- to 15-day-old rats net secretion of calcium was similar in jejunal and ileal segments, while in the 42-day-old rats net secretion was twofold greater in the ileal than jejunal segments. Perfusion of the hypertonic solution almost doubled net secretion of calcium in the jejunal segments at both ages, but had no effect on rate secretion of calcium in the ileal segments. These findings suggest that infants are more prone to lose calcium into the lumen of the intestine than adults, especially during episodes of osmotic diarrhea when oral intake is restricted acutely.

Oral aluminum (Al) exposure is a consequence of the element's presence in food, cosmetics, drinking water and its use in preparations administered therapeutically in large quantities as antacids or phosphate binders. Al is neurotoxic in animals and elevated concentrations of Al have been detected in brains of patients with certain encephalopathies. Protein synthesis, ribosomal RNA content and microtubular polymerization may be altered by Al. Since there are critical periods of protein synthesis and cellular division during embryonic development it was of interest to determine the teratogenic potential of Al. Since parathyroid hormone (PTH) increases tissue Al concentrations the effects of combined treatment of Al and PTH were also evaluated. Rats were maintained on diet supplemented with Al and/or calcium and treated with PTH or vehicle from day 6 of pregnancy through day 19, when fetuses were removed by Caesarean section. Combined or separate treatment with PTH and Al did not alter the number of live fetuses, fetal size, incidence of gross, soft-tissue or skeletal anomalies. Al concentration in whole fetal carcass was not affected. Combined treatment was accompanied by a significant increase in resorption rate. Histopathological alterations were not detected in animals from any treatment group. These results suggest that although combined maternal treatment with PTH and 1000 ppm Al may increase embryolethality, it may not enhance the potential for Al-induced toxic effects in surviving rat fetuses.

Levels of GH, PRL, and insulin in diabetic (db/db) mice were studied by radioimmunoassay. Serial blood samples from normal and diabetic mice of both sexes were obtained by orbital puncture at 5, 7, 10, 15, 20, 24, and 28 weeks of age; the final sample was obtained by decapitation at 32 weeks. Serum insulin and glucose levels in db/db mice were higher than normal throughout the study. Compared to those in normal controls, GH and PRL concentrations in the pituitary gland were 33 to 67% lower in db/db mice at 32 weeks of age. Serum GH levels in orbitally collected samples were also markedly subnormal in male diabetics; in females, the differences were not significant. GH levels in sera collected at 32 weeks were not significantly different from those of controls in either sex. PRL concentrations in the orbitally collected sera of db/db mice were lower than normal until 10-12 weeks of age; after this age the values approached normal levels. PRL concentrations in sera collected at decapitation were significantly lower than normal in db/db mice of both sexes. A single injection of perphenazine elicited a 20-fold rise in serum PRL concentrations in normal females; in db/db females, there were no increases. The results suggest generally deficient secretion of GH and PRL in the mutant db/db mouse.

A vasoactive product of a cell type present in afferent and not efferent lymph has been described. The kinetics of the resultant hyperemia following intradermal injection of the material distinguish this activity from histamine, bradykinin or prostaglandin E₁. Furthermore, the activity appears to be distinct from plasminogen activator and prostaglandins on the basis of studies with DFP and indomethacin. This vasoactive product may mediate blood flow alterations following antigenic challenge. A relationship between antigen-induced increased blood flow and increased lymphocyte traffic has been described for both fixed lymphoid tissue and induced cellular hypersensitivity sites. It is our contention that the regulation of the blood flow to such regions may be of fundamental importance in governing the number of inflammatory cells in an area and the rate of extravasation of blood plasma.

The effect of the angiotensin I converting enzyme inhibitor, SQ-14,225 on DCA-NaCl hypertension was determined. The inhibitor did not affect the development of DCA-NaCl hypertension. It also did not affect the blood pressure of animals with established DCA-NaCl hypertension. This suggests that the SQ-14,225 exerts it's antihypertensive effect purely by decreasing angiotensin II and not by increasing vasodilator kinins.

Mean total body clearances were measured in unanesthetized rats as Dose iv/AUC in which AUC is the area under the plasma radioactivity disappearance curve for [¹⁴C]labeled inulin, PAH, and TEA and also for [³H]inulin. The clearance of inulin radioactivity, either ¹⁴C or ³H, was a satisfactory estimate of glomerular filtration rate. The clearance of [¹⁴C] radioactivity from labeled TEA was a reliable estimate of renal plasma flow. The renal filtration fraction, which was calculated as the ratio of inulin and TEA clearances, varied from 0.15 to 0.30, with a mean value of 0.21 in the 20 rats in which both clearances were measured simultaneously.

Renal plasma flow and glomerular filtration rate can therefore be estimated in the same unanesthetized rat by the clearances of TEA and inulin, calculated as Dose iv/AUC from the disappearance curves of ¹⁴C and ³H plasma radioactivity after a single iv injection containing both [¹⁴C]TEA and [³H]methoxyinulin.

Lead acetate (20 to 40 mg/kg body weight) or mercuric chloride (3 mg/kg body weight) was injected intravenously into normal rats and those pretreated with calcitonin (0.1 mU/g body wt/hr for 1-4 hr). Rats were sacrificed at intervals from 5 min to 24 hr after heavy metal injection. Tibias were prepared histologically, using Okada and Mimura's vital staining technique. The metaphyses and diaphyses were examined under the light microscope to study the effect of calcitonin on the uptake and distribution of these two metals in bone. Calcitonin dramatically reduced the initial uptake of lead and mercury by bone. This reduction, at least for lead, occurred in both trabecular and compact bone. The mechanism(s) by which calcitonin influences the distribution of lead and mercury in bone has not yet been determined.

The isolation of collagenase present in serum-containing medium harvested from bone cultures was effected by heparin-Sepharose affinity chromatography. Almost all of the bone tissue collagenase released into the medium was of the latent, inactive type, which could be activated in vitro with trypsin. Over the course of the experiment a 20-fold greater amount of collagenase was released into the medium by the resorbing cultures stimulated with prostaglandin E₂ as compared to the control cultures. A significant increase in calcium released into the medium correlated in time with rapid bone resorption as measured microscopically. The increase in collagenase activity did not demonstrate the same precise time course.