Modification of vasopressin microvascular responses by endotoxin, endothelin, and nitric oxide

The sensitivity of rat cremaster muscle arterioles to topically applied arginine vasopressin (AVP) is greatly increased by endotoxin (ENDT) [1]. The hypothesis is that the increase in vasoconstrictor sensitivity is in part due to modification of the AVP responses by endothelial compounds such as nitric oxide (NO) and endothelin. Reactivity of left cremaster muscle microvessels of pentobarbital anesthetized Sprague-Dawley rats was measured using videomicroscopy. Femoral arterial pressure as well as second and third order arteriolar (A2 and A3) vasoconstrictor threshold responses were determined for topical AVP (10(-15)-10(-6) M). These measurements were repeated in the presence of ENDT (6 mg/kg) alone and in the presence of the NO synthase inhibitor L-NAME (N omega-nitro-L-arginine methyl ester; 1 mg/kg) and ENDT (group 1). The control threshold (M)(-log) for arteriolar constriction by AVP was 9.4 +/- 0.7. After ENDT the threshold decreased significantly (P < 0.05) to 13.8 +/- 0.5, but returned to 9.0 +/- 0.5 after i.v. injected L-NAME. Acetylcholine (ACh) injected i.a. during AVP constriction significantly increased diameters at control and after ENDT, but not after L-NAME. In group 2 the AVP threshold was determined at control, after L-NAME plus hydroquinone (HQ), and at 30, 90, and 120 min post-ENDT in the presence of L-NAME + HQ. The AVP threshold at control was 9.0 +/- 0.3, after L-NAME 9.0 +/- 0.6, and after HQ 8.0 +/- 0.7. After L-NAME + HQ, the threshold was significantly increased to 7.3 +/- 0.2. After ENDT, in the presence of both antagonists, the threshold remained elevated at 7.4 +/- 0.2.(ABSTRACT TRUNCATED AT 250 WORDS)