PDF《B.P. Setchell2》

heat effects. Introduction The literature on the effects of heat on the testis has already been recently reviewed (Kandeel and Swedloff, 1988, Setchell, 1998, Morgenthaler et al., 1999) but as a great deal of new information has been obtained since 2000, an update would seem to be justified. The testes of many species of mammals descend either during fetal life or shortly after birth into a scrotum, where the temperature is appreciably lower than in the abdomen. However, in some mammals, notably elephants, hyraxes, edentates, insectivores and cetaceans, the testes remain inside the abdomen (see Setchell and Breed, 2006), although in dolphins, the testes appear to be cooled by venous blood from the tail running into the abdominal cavity and next to the arterial supply for the testes (Rommel et al., 1992;

1994). In bulls, as in other animals with scrotal testes, the testes are cooled by countercurrent exchange of heat between the venous and arterial blood in the spermatic cord (Waites and Moule, 1961;

Brito et al., 2004). Heat is lost from the testis and scrotum to the environment through the scrotal skin, which is well endowed with sweat glands (see Setchell and Breed 2006). The temperature on the surface of the scrotum is lower at its base than near the neck, but the temperature inside the testis is almost uniform, even slightly warmer at the base (Kastelic et al., 1996;

1997). In rams, the tunica dartos muscle is involved in moving the testes closer to the body by contracting under cold conditions and further by relaxing when hot. The body-scrotal temperature difference is greater in an environment of 6o C and less at 40o C, although during fever induced by lipopolysaccharide injection or during exercise, scrotal temperature remains constant while body temperature Setchell. Heat and the testis. Anim. Reprod., v.3, n.2, p.81-91, April/June. 2........