Interaction between cholinergic and adrenergic pathways of the hypothalamic ventromedial nucleus on cardiovascular regulation.

In this work we studied the possible interaction between cholinergic (muscarinic and nicotinic) and adrenergic (alpha 1- and beta-adrenergic) pathways of the hypothalamic ventromedial nucleus on the regulation of arterial pressure and heart rate in conscious normotensive rats. Mean arterial pressure and heart rate were recorded in rats with cerebral chronic stainless steel cannulae implanted directly into the ventromedial nucleus. The changes in arterial pressure and heart rate produced by the injection of the cholinergic agonist (carbachol or nicotine) into the ventromedial nucleus were studied before and after the injection of prazosin (an alpha 1-adrenergic antagonist) or propranolol (a beta-adrenergic antagonist) into this same area. The injection of carbachol (2 nmol) or nicotine (40 mmol) into the ventromedial nucleus induced pressor and tachycardia responses. Previous treatment with prazosin or propranolol blocked the pressor response to carbachol and nicotine. Propranolol also abolished the tachycardic response to carbachol or nicotine, but prazosin reduced only the tachycardia produced by carbachol into the ventromedial nucleus. These results show an interaction between cholinergic and adrenergic pathways of the ventromedial nucleus affecting cardiovascular regulation and suggest that the alpha 1- and beta-adrenoceptors of this nucleus are involved in these responses.