Nc. Bennett et al., LH RESPONSES TO SINGLE DOSES OF EXOGENOUS GNRH BY FRESHLY CAPTURED DAMARALAND MOLE-RATS, CRYPTOMYS-DAMARENSIS, Journal of Reproduction and Fertility, 99(1), 1993, pp. 81-86
Pituitary function in reproductive and nonreproductive colony members
of Damaraland mole-rats, Cryptomys damarensis, was investigated by mea
suring the LH responses to single doses of 2 mug exogenous GnRH and ph
ysiological saline in 29 females and 37 males (31 of these animals fro
m two entire colonies). In females, basal LH concentrations were signi
ficantly greater in reproductive (n = 9) than in nonreproductive anima
ls (n = 11): 7.6 +/- 1.0 versus 4.3 +/- 0.6 miu ml-1, respectively (P
< 0.001). Reproductive females had a significantly greater LH response
to 2.0 mug GnRH (7.6 +/- 1.0 to 37.7 +/- 6.2 miu ml-1; n = 9) than di
d nonreproductive females (4.3 +/- 0.6 to 11.8 +/- 1.0 miu ml-1; n = 1
1, P < 0.001). In contrast, there was no significant difference in bas
al LH concentrations between reproductive (n = 8) and nonreproductive
males (n = 20): 5.3 +/- 4.3 versus 3.2 +/- 1.2 miu ml-1, respectively.
There was also no difference in LH response to the administration of
2.0 mug GnRH between reproductive and nonreproductive males (5.3 +/- 4
.3 to 21.8 +/- 8.6 miu ml-1; n = 8; versus 3.2 +/- 1.2 to 21.1 +/- 8.5
miu ml-1; n = 21; P = 0.5). When the results from the two entire colo
nies were analysed separately, LH responses to GnRH in the 11 nonrepro
ductive females were less than in the two reproductive females. In con
trast, the response of two reproductive males in the colonies did not
differ from that of 16 nonreproductive males, although these latter co
mparisons could not be validated statistically. The following conclusi
ons were made. First, the anterior pituitary of nonreproductive female
mole-rats is less sensitive to GnRH than is that of reproductive fema
les, possibly resulting from a lack of priming by endogenous GnRH. Sec
ond, the hypothalamic-pituitary axis is more active in reproductive fe
males, giving rise to higher concentrations of LH in plasma. Thus supp
ression in nonreproductive females is due to inhibition of GnRH render
ing them temporarily infertile. Third, the lack of differentiation in
response to GnRH in males suggests that nonreproductive males are beha
viourally inhibited from breeding.