Effects of Insulin on Vasoconstrictor Responses to Alpha Agonist and Tilting

Abstract

The effects of insulin on vasoconstrictor response were studied in diabetics without autonomic neuropathy. Vasoconstrictor response to phenylephrine was measured before and after insulin injection in 10 diabetics. Mean blood pressure, forearm blood flow, and forearm vascular resistance remained unchanged after insulin administration. But the increase in forearm vascular resistance to phenylephrine decreased significantly and heart rate increased significantly after insulin injection. In 9 diabetics, vasoconstrictor response to tilting was measured before and after insulin injection. Mean blood pressure, cardiac index, and the total peripheral resistance index remained unchanged after insulin administration. However, the increase in the total peripheral resistance index to tilting decreased significantly and heart rate increased significantly after insulin injection. Furthermore, a significant fall in mean blood pressure following tilting was observed only after insulin administration. Although blood glucose levels decreased significantly, no hypoglycemic symptoms occurred. The present study suggests that insulin inhibits vasoconstrictor responses to both alpha agonist and tilting in diabetics.

Mechanisms of Arterial Hypotension After Therapeutic Dose of Subcutaneous Insulin in Diabetic Autonomic Neuropathy

“…Similar results have subsequently been obtained by other investigators (3)(4)(5). This was associated with a decrease in forearm vascular resistance.…”

“…This is indicated by the smaller increase and the paradoxical decrease in FVRs in the standing position after subcutaneous insulin, in subjects without and with AN, respectively (Fig. What is new in this compared with previous studies (1)(2)(3)(4)(5) is that a relevant decrease in BP was observed in subjects with AN after therapeutic doses of subcutaneous insulin closely mimicking the conditions of the real life of diabetic subjects. In subjects with intact SNS, the first hemodynamic effect overrides the second, and BP does not change or tends to increase.…”

“…4). In contrast, in previous studies (1)(2)(3)(4)(5), insulin was given as intravenous boluses, usually in supraphysiological amounts. In contrast, in subjects with AN, the impaired ability to release NE unmasks the insulin inhibition of peripheral vasoconstriction and peripheral vascular resistances and blood pressure decrease.…”

“…Second, therapeutic hyperinsulinemia markedly blunts the vasoconstrictive responses to activation of the SNS in the standing position. This well-known effect of insulin (1-5) has been attributed to vasodilation (4,5,10,18,28,46,47). 4).…”