Effects of Naloxone on Kidney Weight, Macromolecular Constituents of Kidney and Cortisol Secretion in Fetal and Neonatal Pigs

Abstract

Opioids are known to influence organ growth and development as well as the hypothalamo-pituitary-adrenal (HPA) axis. The studies reported in this dissertation were undertaken to evaluate the effects of naloxone on kidney weight, macromolecular constituents of kidney and cortisol secretion in fetal and neonatal pigs and determine if these effects are sex-dependent. Effects of naloxone on kidney weight and macromolecular constituents of kidney: Daily intravenous injections of 1 mg/kg naloxone significantly increased both kidney weight and relative kidney weight of male fetuses. Total DNA and RNA content in treated males was significantly higher than in control males. Interestingly, the protein concentration in treated males was significantly lowered by naloxone. However, no significant difference in total protein content between the two groups was observed. In female fetuses, naloxone had no effects on kidney weight or macromolecular constituents of kidney. Although kidney weight in the treated male fetus was not significantly higher in comparison to the treated female fetus, relative kidney weight in males was statistically significant higher than in females. Interestingly, the concentration of RNA was significantly increased by naloxone in males compared with females. Total RNA content of kidney in the male was also significantly higher than in the female. Moreover, in males protein concentration was significantl! y lower than in females. These findings indicate that during prenatal life naloxone may exert different actions on DNA, RNA and protein synthesis depending on sex. Following significant differences between 1-day-old and 14-day-old control male newborn piglets were observed in (1) kidney weight; (2) total DNA content of kidney; (3) total RNA content of kidney and (4) the ratio of RNA to DNA. Interestingly, these differences were not any more evident when 1-day-old naloxone treated male newborns were compared with 14-day-old naloxone treated male neonates. These results indicate that naloxone affects the kidney development and interferes with DNA and RNA synthesis in male kidney during prenatal life. In 14-day-old neonatal pigs, naloxone pump implantation did not significantly influence kidney weight, relative kidney weight and cellular parameters outlined in the study. The results demonstrate that naloxone increased fetal but not neonatal kidney weight in a sex-dependent manner, and point to a role of hyperplasia in renal weight gain of treated fetal males. Effects of naloxone on cortisol secretion: No sex difference was evident in the effect of naloxone on cortisol secretion. In control pig fetuses, no changes in plasma cortisol levels were observed during the four blood sampling periods on days 102, 104, 106, 108 and 110 of gestation. Intravenous naloxone treatment caused a significant increment in cortisol levels on days 102, 104, 106 and 108 of gestation, but not on day 110. Moreover, naloxone had a chronic stimulatory effect on cortisol secretion over the treatment period, when the levels prior to the treatment (levels before naloxone injection on each day) were compared (days 102 to 110 of gestation). In naloxone-treated fetuses, basal cortisol levels (levels before injections) increased significantly from 54.14 7.03 ng/ml on day 102 to 89.75 12.02 ng/ml on day 108. Thus, there was a significant positive correlation between basal cortisol levels and the period of naloxone treatments (r = 0.296, p < 0.05). From 1 day after birth to 14 days of age, no changes in plasma levels of cortisol were observed in neonates implanted with naloxone pumps. However, unlike controls, cortisol levels in the treated neonate did not decrease significantly with age. These results indicate that naloxone has a chronic stimulatory effect on cortisol release in neonatal pigs. The data illustrate that the HPA axis in fetal and neonatal pigs is most probably under inhibitory influence of opioids.