Exaggerated cardiovascular stress responses and impaired β-adrenergic-mediated pressor recovery in obese Zucker rats

Clinical studies have demonstrated that the pressor response to acute stress is larger in obese versus lean individuals. We therefore tested the hypotheses that the pressor response to behavioral stress is greater in obese ( OZRs) versus lean Zucker rats (LZRs) and that reduced beta-adrenergic-mediated vasodilation contributes to the enhanced pressor response. Animals were restrained and subjected to acute pulsatile air jet stress ( 3 minutes), followed by a poststress period of 20 minutes; beta-adrenergic blockade was achieved with propranolol (5 mg/kg, IV) given 15 minutes before the start of air jet stress. Mean arterial pressure ( MAP) was continuously monitored by telemetry. Untreated OZRs responded with a greater integrated pressor response ( area under the curve [AUC]) to acute stress (41.2 +/- 6.1 versus 21.2 +/- 3.3 mm Hg X 3 minutes, OZR versus LZR; P < 0.05) and significantly reduced poststress recovery of MAP. beta-Adrenergic blockade had no effect on stress AUC in either LZRs or OZRs but significantly attenuated the poststress recovery of MAP in LZRs only ( poststress AUC: -100.1 +/- 48.1 versus 49.0 +/- 13.5 mm Hg X 20 minutes, untreated versus propranolol; P < 0.05). In anesthetized animals, significantly smaller increases in mesenteric vascular conductance contributed to blunted depressor responses to isoproterenol in OZRs versus LZRs, suggesting that beta-adrenergic stimulation causes a greater reduction in total peripheral resistance in lean versus obese animals. We conclude that beta-adrenergic-mediated vasodilation facilitates blood pressure recovery after stress and that this pathway is compromised in an animal model of morbid obesity, resulting in the impaired ability to regulate blood pressure during stress.