The interrelation between hypothalamically induced changes in sympathetic discharge to the gastrointestinal and cardiovascular systems.

In chloralose-anesthetized, adrenalectomized cats, the sympathetically conveyed effects of topical hypothalamic stimulations on gastric volume, blood pressure and heart rate were systematically explored. The vagal nerves were cut but could be kept active by graded efferent stimulation. In the absence of such vagal activity, hypothalamic stimulation had no appreciable influence on gastric volume, even though the stomach maintained considerable myogenic tone. When, however, a vagal excitatory activity was present, hypothalamic stimulation could markedly affect gastric tone, indicating that the sympathetic fibres exert their inhibitory influence on the stomach via its cholinergic intramural neurons. Hypothalamic stimulations that induced reductions in pressure or heart rate also usually caused an enhancement of gastric tone. Similarly, pressor responses were associated with decreases in gastric volume whereas stimulation-induced tachycardia was not linked to any particular type of gastric response. Thus, the hypothalamic sympathoinhibitory influences on the cardiovascular system seem closely connected to a supression of the sympathetic outflow to the stomach. There is, on the other hand, no regular association between hypothalamic sympathoexcitatory influences on the cardiovascular and gastrointestinal systems; in fact, there is in many areas even a suppression of sympathetic discharge to the stomach in association with cardiovascular stimulation.