CONTRACTILE RESPONSES TO VARIOUS STIMULI IN ISOLATED RESISTANCE VESSELS FROM SIMULTANEOUSLY HYPERTENSIVE AND STREPTOZOTOCIN-DIABETIC RATS

Diabetes mellitus and hypertension are common chronic diseases that fr equently occur simultaneously. The induction of streptozotocin (STZ) d iabetes mellitus in spontaneously hypertensive rats (SHR) offers the o pportunity to investigate the influence of both entities in a reproduc ible manner. We investigated the effects of various vasoconstrictors o n isolated small arteries from the mesenteric vascular bed of normoten sive rats (Wistar-Kyoto rats, WKY) and SHR with chronic (8 weeks), STZ -induced diabetes mellitus. No consistent changes in hemodynamic param eters of the (STZ-) normotensive and (STZ-) hypertensive rats were not ed. The K+-normalization procedure yields the individual optimal lumen diameter, which was the same for the arteries of the four groups of r ats. The passive wall tension resulting from this normalization proced ure was higher only in preparations from the control hypertensive grou p as compared with those from the control normotensive rats. Morpholog ical investigations showed that small arteries from control SHR had an increased tunica media thickness as compared with those of control WK Y; the STZ-WKY had an increased tunica media thickness as compared wit h preparations from control WKY. The vasoconstriction caused by alpha( 1)-adrenoceptor stimulation [norepinephrine (NE), methoxamine] and ser otonin is unchanged in chronic experimental diabetes. The diabetic sta te reduced the sensitivity [-log EC(50)(M)] for the concentration-resp onse curves (CRC) of calcium chloride. The CRC of potassium chloride i ndicated the same sensitivities, but maximal active wall tensions of v essels from STZ-SHR were reduced as compared with those from STZ-WKY. The well-known enhancement of the effects of various contractile stimu li caused by hypertension could not be demonstrated for the isolated s mall arteries used in the present study, although a nonsignificant ten dency was observed. However, the STZ-diabetic state did not cause impo rtant additional pharmacodynamic changes, despite the morphological al terations in those vessels.