β-adrenergic receptor blockade during exercise decreases intestinal lymphocyte apoptosis but not cell loss in mice

Abstract

Catecholamines induce apoptosis in various lymphoid populations. This process can occur with both α- and β-adrenoreceptors. Heavy exercise increases plasma catecholamine concentrations, and is also a cause of lymphocyte apoptosis, a possible explanation for postexercise lymphocytopenia. The purpose of this study was to examine the effects of adrenoreceptor antagonism on exercise-induced decreases and apoptosis of intestinal lymphocytes. Mice received an intraperitoneal injection of phentolamine (a nonselective α-blocker), nadolol (a nonselective β-blocker), or saline (vehicle) prior to an exhaustive bout of exercise. Total intestinal lymphocyte numbers, percent and number of CD3+ lymphocytes, and cell viability were assessed. Neither α- nor β-antagonism prevented exercise-induced cell loss in the intestine; however, pretreatment with nadolol significantly reduced the number of apoptotic and necrotic cells. Phentolamine administration appeared to increase the incidence of cell death among intestinal lymphocytes. Both drugs decreased the percentage of CD3+ intestinal lymphocytes. Our study suggests that catecholamines are not responsible for postexercise lymphocytopenia, but β-adrenoceptor blockade may confer protection against exercise-induced apoptosis of intestinal lymphocytes.Key words: catecholamines, exhaustive exercise, apoptosis, intestinal lymphocytes, rodents.