LH Responses of Female Naked Mole-rats, Heterocephalus Glaber, to Single and Multiple Doses of Exogenous GnRH

To investigate possible differential pituitary secretion of LH in breeding and non-breeding female naked mole-rats, the LH responses to administration of exogenous GnRH were measured in 55 females from 20 captive colonies. Single doses of 0.1, 0.5 or 1.0 micrograms GnRH produced a significant rise in plasma LH concentrations 20 min after s.c. injection in breeding and non-breeding females at all doses (P less than 0.001). While at the highest dose of 1.0 microgram there was no difference in the LH response between breeding and non-breeding females, as the dose was lowered there was a progressive decline in the LH response in non-breeding females such that, at the 0.1 microgram dose, GnRH produced only a small, but significant, increase in plasma LH (1.3 +/- 0.2 to 2.9 +/- 0.5 mi.u./ml, N = 5) compared with breeding females (3.4 +/- 0.8 to 9.6 +/- 2.0 mi.u./ml, N = 6). The LH responses of the latter were not significantly reduced at the lower doses of GnRH. The apparent lack of sensitivity to low doses of exogenous GnRH in non-breeding females was reversed by 4 consecutive 1-h injections of 0.1 microgram, which produced a rise in LH from 1.2 +/- 0.2 to 9.0 +/- 0.2 mi.u./ml (N = 4), comparable to that of breeding females given a single injection of 0.1 microgram GnRH. These results suggest that the anterior pituitary in non-breeding female naked mole-rats is less sensitive to low doses of exogenous GnRH than in breeding females, possibly due to a lack of priming by endogenous GnRH. Therefore, the socially-induced block to ovulation in non-breeding female naked mole-rats may be due to inhibition of hypothalamic GnRH secretion.