EFFECT OF HYPOTHALAMIC DEAFFERENTATION ON THE PULSATILE SECRETION OF LUTEINIZING-HORMONE IN OVARIECTOMIZED LACTATING RATS

The pulsatile luteinizing hormone (LH) secretion in ovariectomized lactating rats bearing complete (CD), anterior (AD), anterolateral (ALD), posterior (PD), or roof (RD) deafferentation of the hypothalamus was determined. All lactating rats were ovariectomized on Day 2 of lactation (Day 0, day of parturition). The deafferentation of nerve fibres to the mediobasal hypothalamus was performed on Day 6 or 7 of lactation. Twenty‐four h after the surgery, blood samples were taken through the indwelling atrial catheter every 6 min for 3 h. Plasma concentrations of LH and prolactin (PRL) were measured by radioimmunoassay. The loss of LH pulses associated with lactation was still apparent following AD, PD and sham‐deafferentation (SD); pulsatile LH secretion was, however, present in rats with CD, ALD and RD despite continued suckling. The only significant difference in plasma PRL concentrations among the various groups was a reduction in the PRL level in rats with RD in comparison to those with SD. We conclude that the neural signal responsible for the inhibition of pulsatile LH release by suckling is conveyed through the dorsal part of the hypothalamus and PRL does not mediate the suppression of LH pulses in mid‐lactation. Copyright © 1990, Wiley Blackwell. All rights reserved