Regulation of ram scrotal temperature during heat exposure, cold exposure, fever and exercise

1. We measured body core and scrotal temperatures (Tbody and Tscrotum, respectively) of rams during 5 h of hot (40 degrees C) and cold (6 degrees C) exposure, for 6 h following intravenous injections of saline (0.9% NaCl) or 0.4 micrograms kg-1 of the purified lipopolysaccharide endotoxin of Salmonella typhosa (LPS), during 40 min of treadmill exercise, and for several days in their pens. 2. At 20-23 degrees C ambient temperature there were significant, but out of phase, circadian variations in Tbody and Tscrotum. Tscrotum was 3.30 +/- 0.03 degrees C lower than Tbody on average. 3. During cold exposure the tunica dartos muscles contracted, nevertheless Tscrotum fell and Tbody-Tscrotum increased. During heat exposure the tunica dartos muscle relaxed and scrotal sweat glands were activated, nevertheless Tscrotum rose and Tbody-Tscrotum decreased. There was no change in Tscrotum after LPS injection or during exercise, but Tbody increased in both cases. 4. We suggested that Tscrotum is regulated independently of Tbody via a feedback circuit involving scrotal thermoreceptors and effectors in the form of tunica dartos muscle activity and scrotal sweat gland activity. This local circuit is not affected by adjustments to the general thermo-regulatory control system during fever. The effector mechanisms were insufficient to maintain Tscrotum during the extremes of heat and cold exposure.