BLOOD LUTEINIZING-HORMONE AND PROLACTIN CONCENTRATIONS IN RESPONSE TONALTREXONE CHALLENGE - STUDIES ON RATS WITH DIABETES-INDUCED BY DIFFERENT DOSES OF STREPTOZOTOCIN

Opiate system involvement in diabetes induced by three different doses of streptozotocin (STZ; 40, 50, and 60 mg/kg body weight [BW]) was st udied by monitoring luteinizing hormone (LH) and prolactin (PRL) level s as a response to naltrexone (Nalt) administration. After four weeks of diabetes a marked decrease in BW, as well as severe hyperglycemia a nd increased blood urea nitrogen (BUN) levels were found. The rats, wh ose diabetes was induced by 50 mg/kg of STZ, exhibited the highest amo unt of blood glucose (P < 0.05, compared with the 40 mg/kg induced gro up) and BUN levels (P < 0.004 compared with the other two groups) and BW loss. The normal response to Nalt, which is expressed by elevation of plasma LH and decreased plasma PRL levels was observed only in the low-dose STZ (40 mg/kg BW) diabetes-induced group, while in the other two diabetic groups (50 and 60 mg/kg BW) there was no significant chan ge in plasma LH and PRL as a result of the Nalt challenge. Presensitiz ation of the endogenous opioid receptors by morphine in normoglycemic (control) and ''low-dose diabetic'' rats (40 mg/kg BW of STZ), present ed a clear difference between the two. Morphine pretreatment inhibited LH response to Nalt in the low-dose, STZ-induced diabetic rats, while no effect of morphine pretreatment on LH response to Nalt could be re corded in the normoglycemic group. Thus it can be concluded that in ST Z-induced diabetes, plasma glucose and BUN levels do not reflect the n euroendocrine injury observed when monitored by LH and PRL secretion i n response to Nalt challenge. Supersensitization of the opioid recepto rs before the Nalt challenge may increase the ability to reveal neuroe ndocrine system impairment.