Intrascrotal Temperature, Testicular Histology and Fertility of Heat-Acclimatized Rats

Abstract

Heat-acclimatized rats were exposed to an ambient temperature of 35\s=deg\C, and the effect on testicular histology, reproductive capacity and body and scrotal temperature was evaluated. Both deep body and intrascrotal temperatures of these animals were found to be higher than those of control rats maintained at 22\s=deg\C.The intrascrotal temperature in the heat-acclimatized animals and the deep body temperature in the controls were similar. Breeding experiments proved the heat\x=req-\ acclimatized animals to be capable of mating and reproducing, although at a lower rate than the controls. The heat reduced only the mating rate and fertilization. After conception, the groups showed no difference. Histological screening revealed degenerated seminiferous tubules randomly scattered in the testes of the heat-acclimatized rats although most of the tubules showed normal spermatogenesis. These localized necrotic foci resemble the overall appearance of a cross-section of a cryptorchid testis. The heat-acclimatized animals, however, maintain a body to scrotum temperature gradient which enables spermatogenesis to proceed despite the elevated temperatures.

Factors for consideration in the interpretation of the adverse effects of elevated environmental temperatures on reproduction in the male rat

“…In contrast to cryptorchid animals, body-to-testis temperature-gradient is maintained in the heat-exposed rats (I.8 ° C) and resembles that of controls (1.4 ° C). The rise in testicular temperature goes hand in hand with histological damage, namely necrotic tubules scattered among normal seminiferous tubules (Bedrak, Samoiloff and Sod-Moriah, 1973;Sod-Moriah, Goldberg and Bedrak, 1974). These necrotic tubules resemble, in their appearance, those found in cryptorchid testis which are characterized by complete aspermia (Llaurado and Dominguez, 1963;Amatayakul et al, 1971;Bedrak, Samoiloff and Sod-Moriah, 1973).…”

“…Exposure of sexually mature young male rats to ambient temperatures exceeding their thermo-neutral point (33-35 ° C) for 3-5 weeks leads, inter alia, to a rise in both body and scrotal temperatures (Sod-Moriah, Goldberg and Bedrak, 1974). Consequently the testicular temperature of heat-exposed rats is higher than controls (which are kept at an environmental temperature of 20-22 ° C) and is similar to that of cryptorchid testis.…”

Effect of neonatal or adult heat acclimation on testicular and epididymal morphometry and sperm production in rats

“…Most studies concentrate on the effect of acute heat shock applied directly to the testes [1][2][3]. Studies on the long-term effect of increased body temperature on sperm production in mammals are rare [4], but they showed that long-term heat acclimation is less deleterious for testicular function then acute heat shock. Moreover, it was demonstrated that non-reproductive parameters (i.e., physiological and transcriptomic) differ between short-and longterm heat acclimated rats [5,6].…”

Role of the pineal gland in male rats chronically exposed to increased temperature

“…High ambient temperature of 32--34 ~ brought about decreased pineal activity of the melatonin-forming enzymes hydroxyindole-O-methyltransferase and N-acetyltransferase (Nir et al, 1975;Nir and Hirschmann, 1978). Sod-Moriah et al (1974) reported that an ambient temperature of 35 ~ had an adverse effect on the reproductive systems of heat adapted male rats. It is generally agreed that the pineal gland acts as an endocrine transducer of photic stimuli, exerting an inhibitory effect on gonadal function.…”