Influence of perivascular adipose tissue on rat aortic smooth muscle responsiveness

Virtually every blood vessel in the body is surrounded to some degree by adipose tissue. A potential role for perivascular adipose tissue as a neurohumoral regulator of vascular responsiveness was studied. Thoracic aortae obtained from male Sprague-Dawley rats were cut into rings for use in a standard in vitro smooth muscle bath set-up. The vessels were either cleaned of surrounding adipose tissue or left intact. Contractile responses to KCl and phenylephrine as well as relaxation responses to acetylcholine, isoproterenol and sodium nitroprusside were not different between cleaned and intact tissues. However, a significant decrease in the sensitivity to norepinephrine was observed in intact vessels. This altered response was corrected by prior treatment with desipramine plus deoxycorticosterone. Contractile responses of aortic ring preparations to tyramine and a potassium-free physiological solution were significantly greater in intact tissues. Electrical stimulation resulted in no response in cleaned tissues, however, a frequency-dependent contraction was elicited in intact vessels. Phentolamine blocked the contractile responses generated by these manipulations which activate the sympathetic neuroeffector system. Responses evoked by electrical stimulation in intact vascular preparations were significantly attenuated by prior exposure to the selective angiotensin II (AII) antagonist Sar-Ile-AII. These observations demonstrate that perivascular adipose tissue significantly influences vascular responsiveness in the in vitro setting.