Contractile physiology and response to temperature changes of the tunica dartos muscle of the rat.

We show here that explants of tunica dartos smooth muscle from the rat scrotum contract in response to cooling. The tension developed during cooling was potentiated by the presence of the overlying skin. This potentiation remained even if direct connection between the muscle and skin was severed by cutting the skin from the muscle but leaving the muscle and skin in contact. The potentiation did not depend on any inherent response of the skin since isolated skin showed no change in tension with cooling. The muscle exhibited a sigmoid dose response to noradrenaline with an EC(50) (dose for 50% contractile response) of 1.03+/-0.02 x 10(-6) M. Acetylcholine altered neither resting tone or the sustained contraction induced by a submaximal dose of noradrenaline. The contractile response to an EC(50) and maximal dose of noradrenaline was attenuated at both 15 and 40 degrees C relative to the response observed at 33 degrees C. We hypothesise that the potentiation of tunica dartos muscle contraction with cooling caused by the presence of the scrotal skin depends on some soluble agent released from the skin and affecting the underlying muscle. Noradrenaline release from the skin, or some molecule with alpha-receptor activity, may account for a small proportion of the potentiation. The remainder of the effect does not depend on prostaglandins, or other products of the cyclooxygenase cascade, or the nitric oxide system.