Uterine Response to Adrenergic Nerve Stimulation in the Guinea Pig1

Open Access
Publisher Website
Google Scholar
Abstract
The effects of hypogastric nerve stimulation on the uterus in the anesthetized guinea pig in estrus are described. Electrical stimulation at frequencies between 1 and 30 pulses per second (pps) with an intensity of 1.5 mA and pulse duration of 1.5 msec for periods up to 5 min causes either an initiation of or an increase in uterine motility. These effects of nerve stimulation are prevented by an alpha adrenoceptor blocking agent (phentolamine 5 × 10−6 g/kg iv). Uterine responses to nerve stimulation at frequencies above 15 pps were not maintained, probably because of the accompanying vascular changes in the uterus. Stimulation of the hypogastric nerves at frequencies between 1 and 6 pps and a lower intensity (1.0 mA) does not elicit uterine contractions per se, but instead increases uterine sensitivity to oxytocin. This increase in sensitivity is slight during stimulation at 1 pps, but becomes highly significant (p < .001) during stimulation at 4 and 6 pps. These results provide indirect evidence that adrenergic nerve impulses can modulate the sensitivity of the myometrial cells to oxytocin. The increase in uterine sensitivity to oxytocin during hypogastric nerve stimulation at 4 pps (1.0 mA) is abolished by an alpha adrenoceptor blocking agent (phentolamine 5 × 10−6 g/kg iv) and potentiated by a beta adrenoceptor blocking agent (propranolol 5 × 10−6 g/kg iv). Therefore, the increase in sensitivity is mediated by interaction of the neurotransmitter norepinephrine with alpha (stimulatory) adrenoceptor sites in the myometrium. The ganglion-blocking agent hexamethonium (5 mg/kg iv) prevents the increase in uterine sensitivity to oxytocin during hypogastric nerve stimulation. These results show that the increase in sensitivity is mediated by stimulation of preganglionic fibers in the hypogastric nerves. One physiological function of adrenergic nerve activity in the myometrium might be a modulation of myometrial excitability to oxytocin and possibly to other agents as well.

This publication has 0 references indexed in Scilit: