Relation in rat hind-limb blood vessels between nervous vasomotor tone and the response to vasoconstrictor drugs

When the nervous component of the vasomotor tone of the blood vessels of the innervated rat hind limb perfused with blood was reduced by ganglion blockade, by section of the nerves to the hind limb, or by the indirect effect of drugs, the vasoconstrictor response of the blood vessels to noradrenaline was immediately increased. This increased peripheral response was observed only when the blood perfusing the hind limb was from the same animal or from a genetically similar animal. Reduction of the nervous component of the vasomotor tone also increased the constrictor response of the hind-limb blood vessels to adrenaline, ephedrine, tyramine and 5-hydroxytryptamine, but did not increase the response to angiotensin, vasopressin or S-methyl isothiourea. Pre-treatment with reserpine increased the hind-limb response to noradrenaline but reduced the response to ephedrine, tyramine and 5-hydroxytryptamine. The results suggest that, in rats, activity in the sympathetic nervous system directly influences the reactivity of peripheral blood vessels to noradrenaline and other sympathomimetic drugs.

Vascular and sweating responses to regional heating of the body surface

The significance of cutaneous and internal thermoreceptors in human temperature regulation was studied by exposing the subject simultaneously to environmental temperatures of 25 and 60 C. Cutaneous, rectal, and tympanic membrane temperatures were recorded along with sudomotor and vasomotor responses. Heat stress to the lower half of the body was accompanied by marked differential vasomotor responses and a pronounced caudal-to-rostral recruitment of sweating in spite of an unchanging or declining tympanic membrane temperature. Heating the upper half resulted in essentially the same vasomotor and sudomotor responses but with significant alteration in the time course and intensity of the sweat recruitment pattern. With sudden lowering of the ambient temperature, sweating on all areas disappeared while internal temperatures remained unchanged. It is clearly demonstrated that under the given experimental conditions both cutaneous and internal thermoreceptors play a significant role in human temperature regulation and that the hypothalamus is not the sole moderator of internal temperature control.

Submitted on July 16, 1961