Effect of fasting on vascular contractility in lean and obese Zucker rats

We compared the effects of fasting (36 h) on blood pressure and aortic contractile responsiveness in lean and obese Zucker rats. Fasting of lean animals resulted in a significant loss in body weight (−9.1 ± 0.1%) and reduction in systolic blood pressure (−11.4 ± 1.9 mmHg). Fasting plasma triacylglycerols (−76%) and beta-hydroxybutryic acid (β-HBA) (+ 218%) were significantly decreased and increased, respectively. The fasting plasma concentrations of insulin (−72%) were significantly decreased, whereas glucose and epinephrine (Epi) were not changed in lean rats. The fasting of obese rats also resulted in weight loss (−5.6 ± 1.3%) but did not cause a significant reduction of blood pressure. The plasma total cholesterol (+18%) was increased, triacylglycerols (−42%) were decreased and β-HBA levels were unchanged in fasted obese rats. Similar to lean animals, the insulin levels of fasted obese rats were significantly decreased (−85%), whereas glucose and Epi concentrations were not significantly changed. Fasting of lean animals had no effect on the maximal contractile response of aortae to high K+ and phorbol 12, 13 dibutyrate (PDBu) but significantly reduced the response to norepinephrine (NE) (% reference: fed, 61.1 ± 11.0; fasted, 45.6 ± 4.5). In addition, the concentration for half-maximal response (ED50) to NE was increased in fasted lean rats (fed, 1.8±0.2×10−8 M; fasted, 3.0±0.3×10−8 M). By comparison, fasting of obese rats had no significant effect on the contractile response to K+, NE, or PDBu. The results show that short-term food withdrawal induces significant changes in vascular contractile properties of lean but not obese rats. Because fasting-induced changes were variable depending on the agonist, the results further suggest that the mechanism did not involve a general loss or enhancement in functional status.