BEHAVIORAL ACTIVITIES AND CARDIOVASCULAR FUNCTIONS: EFFECTS OF HEXAMETHONIUM ON CARDIOVASCULAR CHANGES DURING STRONG SUSTAINED STATIC WORK IN RHESUS MONKEYS

¹ Laboratory of Psychobiology, Department of Psychiatry and Department of Physiology, Harvard Medical School, Boston, Massachusetts

Rhesus monkeys have been trained to pull with a force of about 80% of their body weight. During pulls, there was a sustained increase in mean arterial blood pressure of about 20 mm Hg and a longer lasting increase in heart rate. Hexamethonium i.m. caused a dose-dependent decrease in resting mean arterial pressure to an asymptote at 40 to 50 mm Hg with doses of hexamethonium of 10 mg/kg or larger. The rise in mean arterial blood pressure during a pull was not attenuated by hexamethonium in doses which prevented the increase in heart rate. Neither atropine nor phentolamine after hexamethonium prevented the pressor response to pulling. It appears, therefore, that the pressor response does not require mediation by the autonomic nervous system. It is suggested that the blood pressure increase during ganglionic blockade is due to mechanical factors related to the contraction of the skeletal muscles. The large cardiovascular effects of skeletal muscle contraction, even in a relatively motionless subject, make the inference of direct environmental or emotional effects on cardiovascular function hazardous.