Apomorphine-Induced Inhibition of Episodic LH Release in Ovariectomized Rats with Complete Hypothalamic Deafferentation 1

Summary

Complete neural deafferentation of the MBH in 53 rats resulted in a constant vaginal diestrous smear pattern in 85% of the rats, and in this type animal very low blood LH levels and absence of episodic LH release followed ovariectomy. The remaining 15% had a constant vaginal estrous smear pattern, and most demonstrated pulsatile LH secretion following ovariectomy. Thus, afferent input to the MBH seems to be required in most rats to sustain episodic LH secretion. Administration of apomorphine, a dopamine receptor stimulator, to animals which were in constant estrus before ovariectomy, resulted in inhibition of pulsatile LH secretion, suggesting that this apomorphine-induced inhibition is a result of activation of dopamine receptors within, rather than outside, the MBH-pituitary unit.

We would like to thank Brad Garibaldi, Bob Schlegel, Veronica Lickova and Cindy Voytek for their help in these studies, and Annette Lowe and Linda Delucchi for preparation of the figures and typing the manuscript. Thanks also to Dr. G. Niswender for anti-ovine LH No. 15, Dr. H. Papkoff for highly purified ovine LH No. G3222B for iodination, Dr. J. Garcia for goat antiserum against rabbit gammaglobulin, and Dr. A. F. Parlow and the NIAMDD for the rat LH used as a reference preparation.