Maturation of the reproductive system in male rats raised at a low ambient temperature

Abstract

Beginning on Day 2 (day of birth = Day 1) rats were raised either in a cold room maintained at 10°C or at 22°C, under identical lighting regimens (LD 12:12). Litters had identical compositions (4 males and 4 females). All animals were weaned and separated by sex on day 25. Groups of males were decapitated on Days 28, 35, 43, 49, 54, 60, 75 and 90. Serum concentrations of LH, FSH and total androgens were determined by radioimmunoassay. Wet weights of seminal vesicles, prostates and testes were determined and the testes examined histologically for the presence of sperm. Serum FSH showed no differences as a function of temperature. Values in both environments were elevated (approximately 1350 ng/ml) between Days 35 and 60 compared to the other times examined (approximately 1000 ng/ml). Serum LH was elevated (>45 ng/ml) on Days 28 and 35 in control animals and on Days 35, 43 and 49 in cold-raised rats. At other times LH was depressed (<35 ng/ml). Total serum androgens showed no pattern. Relative testicular weight was maximal between Days 43 and 54 in control animals and between Days 49 and 60 in cold exposed animals. Mature sperm were found in 46.0 ± 6.78 percent of the seminiferous tubules of control animals on Day 35 and in 98.0 ± 2.0 percent of the tubules on Day 43. In cold-raised animals 18.0 ± 7.35 percent of the tubules contained sperm on Day 35 and 73.3 ± 7.15 percent on Day 43. Accessory organ growth rate seemed to increase between Day 43 and 49 in control animals but not until between Day 49 and 54 in cold exposed rats. Low ambient temperature thus appeared to delay sexual maturation in the male rat. This delay may be the result of a delay in the appearance of an LH 'surge' or by a depression in prolactin or a change in some other as yet unidentified hormone.