Effect of warm-rearing and heat acclimation on pituitary-gonadal axis in male rats

Plasma gonadotrophic and testicular hormones concentrations in both immature and adult male rats exposed to 34 degrees C of ambient temperature were determined. In vitro steroidogenic ability of interstitial cells from experimental rats was also studied. Four groups of rats (n = 45) were used. Warm-reared (WR) males were housed in 34 degrees C and control-reared rats in 20 degrees C from birth to adulthood. The other groups were acclimated to 34 degrees C [warm-acclimated (WA) group] or 20 degrees C [deacclimated (DA) group] as adults. Decreased body weight and testis weight (p < 0.05) was found in heat-exposed groups, but relative testis weight was unchanged in WA and increased (p < 0.05) in WR and DA males. Plasma luteinizing hormone (LH) concentration increased in WA and DA males. Increased (p < 0.05) follicle-stimulating hormone (FSH) and prolactin plasma levels were found in DA and WR groups respectively. WA males had decreased testosterone (T) and WR rats androstenedione (A(4)) plasma concentration (p < 0.05). Interstitial cells (43% of them were Leydig cells by 3 beta-hydroxysteroid dehydrogenase activity) from heat-exposed males secreted less (p < 0.05) T compared with the control group when incubated without LH (basal conditions). Androstenedione secretion decreased (p < 0.05) in WA rats. Secretion of estradiol-17 beta (E-2) was higher in WR and lower in DA cells under basal conditions. Weaker responsiveness to LH was observed in WR cells. Androgen synthesis from pregnenolone by interstitial cells increased (p < 0.05) in the WA group. We concluded that heat exposure of neonatal and adult male rats caused different pituitary-testicular axis adjustments. It seemed that long-term heat exposure of neonatal rats is less deleterious concerning the activity of pituitary-testicular axis than heat acclimation of adults.