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

Abstract

Complete neural deafferentation of the MBH [medial basal hypothalamus] 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 [lutropin] 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. 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.