Prolactin Release during Exercise in Normal and Adrenodemedullated Untrained Rats Submitted to Central Cholinergic Blockade with Atropine

Abstract

To study the role of the central cholinergic system in pituitary prolactin (PRL) release during exercise we injected atropine (5 × 10−7 mol) into the lateral cerebral ventricle of intact or adrenodemedullated (ADM) untrained rats, at rest or submitted to exercise on a treadmill (18 m · min−1, 5% grade) until exhaustion. The rats were implanted with chronic jugular catheters for blood sampling and with unilateral intracerebroventricular (icv) cannulas placed in the right lateral ventricle. Blood prolactin concentrations were measured before and every 10 min after the start of exercise for a period of 60 min. After the animals started running, plasma prolactin levels rose rapidly in both normal and ADM rats, reaching near maximum at 10 min. Close to exhaustion (19.8 ± 2.9 min for intact rats and 23.5 ± 4.1 min for ADM) they were still high, remained increased until 30 min, and returned to preexercise levels at 40 min. Icv injections of atropine decreased the time to exhaustion by 67% in intact rats and by 96.2% in ADM and also reduced the exercise-induced PRL release in both intact (50%) and ADM rats (90%). The results showed that prolactin release induced by exercise was dependent on the exercise workload and could be observed as early as after 10 min of running, remaining increased until 30 min. These data indicate that adrenodemedullation does not affect prolactin secretion induced by exercise, although adrenodemedullated rats proved to be more sensitive to the reducing effect of central cholinergic blockade on their maximal capacity for exercise.