Sm. Hileman et al., EFFECT OF INHIBITING 5-ALPHA-REDUCTASE ACTIVITY ON THE ABILITY OF TESTOSTERONE TO INHIBIT LUTEINIZING-HORMONE RELEASE IN MALE SHEEP, Biology of reproduction, 50(6), 1994, pp. 1244-1250
The extent to which inhibitory effects of testosterone (T) on LH secre
tion in the ram are mediated by its metabolite dihydrotestosterone (DH
T) is unknown. Our objective was to determine the effect of inhibiting
5 alpha-reductase activity on pulsatile patterns of LH release in cas
trated, T-treated male sheep. Nine Dorset and six Hampshire castrated
male sheep were allocated equally to one of three treatment groups: 1)
infusion of T (768 mu g/kg/day), 2) infusion of the reductase inhibit
or (RI) L-651,723 (0.6 mg/kg/day), and 3) T+RI infusion. Treatments we
re continuously infused for 3 days. Blood samples were collected via a
n indwelling jugular catheter at 10-min intervals for 4 h immediately
prior to (Day 0) and during the final 4 h of infusion (Day 3). Changes
in mean LH, LH pulse amplitude, LH interpulse interval(IPI), T, 17 be
ta-estradiol(E), and DHT were derived for each animal by subtracting v
alues for Day 0 from Day 3. Data were subjected to one-way analysis of
variance. The increase in T and E after infusion of T was similar (p
> 0.10) in T- and T+RI-treated males and greater (p < 0.01) than in RI
-treated males. The increase of DHT was greater (P < 0.01) in T-treate
d than either T+RI- or RI-treated males whereas the change was similar
(P > 0.10) for T+RI- and RI-treated males. T decreased mean LH more (
P < 0.01) than RI, T+RI. suppressed mean LH more (P < 0.01) than RI bu
t not as much (P < 0.01) as T alone. The LH IPI was longer (p < 0.05)
in T-treated males than in RI-treated males. The LH IPI for T+RI-treat
ed males was intermediate between those in RI-treated (p = 0.06) and i
n T-treated (P > 0.10) males. Changes in LH pulse amplitude were simil
ar (p > 0.10) for T- and RI-treated males and for T+RI- and RI-treated
males. However, LH pulse amplitude was increased (p < 0.05) by T+RI t
reatment compared to T treatment alone. We conclude that the conversio
n of T to DHT by 5 alpha-reductase represents a physiologically import
ant step whereby T inhibits LH secretion in the ram.