In vitro interstitial (Leydig) cell response to LH and concentrations of plasma testosterone and LH in the naked mole rat (Heterocephalus glaber, Ruppell)

Abstract

Reproductive endocrinology of the male naked mole rat (Heterocephalus glaber) caught in the wild was studied. In vitro treatment of isolated Leydig cells using either normal dose of LH capable of stimulating mice Leydig cells (0.093–3 mIU/ml) or a relatively high dose (25 mIU/ml) evoked very little response with respect to testosterone production. When similar doses were used to stimulate mice Leydig cells, there was a clear and marked graded increase in testosterone production corresponding to the concentration of LH. Plasma LH and testosterone levels were also measured and found to be 2.0 f 0.24 mIU/ml and 26–09 f 5.70 nmol/l, respectively. Whereas the plasma level of LH was low, that of the testosterone was quite high compared to other animals.

In view of low plasma LH levels, it is probable that the suppression is at the level of the hypothalamus such that release of gonadotrophin releasing hormone (GnRH) is greatly reduced. However, this low plasma LH quickly saturates the receptor sites in the Leydig cells leading to rapid production of testosterone by this large volume of cells whose cumulative manifestation is a high level of plasma testosterone. Although this level of testosterone is considered high, it is not high enough to trigger spermatogenesis. These in vitro results seem to support the suggestion that the receptor sites on the plasma membrane of these Leydig cells are easily saturated such that no further treatment with LH would yield a significant response.