NALOXONE ADMINISTRATION DOES PLOT RELIEVE THE INHIBITION OF GONADOTROPIN-RELEASE IN FOOD-RESTRICTED, LACTATING RATS

Lactational anovulation is an important factor in determining birth sp acing in women living in developing countries. Therefore, a more compr ehensive understanding of the mechanisms involved in the relationships among lactation, nutrition and ovulation is important. This study was designed using the food-restricted, lactating rat to examine whether endogenous opioids might be invoked in depressing gonadotropin release . Females were mated after 65 d of age and, beginning on d 42 of life, offered food in unrestricted amounts (control) or were food restricte d to 50% of what the controls consumed. On d 15 of lactation, dams wer e injected with either naloxone hydrochloride (3 mg/kg body weight) or saline and killed 0, 15, 30 or 60 min later. Plasma was analyzed for luteinizing hormone, follicle-stimulating hormone and prolactin. Food restriction decreased plasma concentrations of luteinizing hormone and follicle-stimulating hormone (P < 0.005). Naloxone administration mar ginally influenced follicle stimulating hormone (P < 0.1), but not lut einizing hormone concentration regardless of diet group. The interacti on among diet group, drug group and time of killing was significant fo r plasma prolactin concentration (P < 0.05). Food restriction lowered prolactin concentrations, but this effect was diminished with increasi ng time after injection of naloxone. Furthermore, the magnitude of the effect of food restriction was lessened and even reversed with treatm ent of naloxone. These results indicate that endogenous opioids are no t the primary mechanism suppressing luteinizing hormone release in foo d-restricted lactating rats.