Mahlon M. Wilkes

Augmentation by naloxone of efflux of LRF from superfused medial basal hypothalamus

The effects of naloxone and β-endorphin (β-EP) on the efflux of luteinizing hormone releasing factor (LRF) from superfused rat medial basal hypothalamus (MBH) were determined. After an equilibration period of 2.5 hrs with Medium 199 at 37°C 0.5 ml fractions were collected. Infusion of medium containing 150 mM KCl for 10 min produced a prompt 4-fold rise in LRF efflux. Injection of naloxone, but not medium alone, into the system significantly increased the effluent concentration of LRF from female (N = 6) MBHs by 177% (P < 0.01) and from male (N = 5) MBHs by 108% (P < 0.05). Administration of β-EP did not significantly alter LRF efflux. However, β-EP did nullify the LRF-stimulating effect of naloxone, when an equimolar mixture of β-EP and naloxone was injected. We conclude that naloxone-sensitive opiate receptors exert a tonic inhibitory effect on tuberoinfundibular LRF neurons. This action does not require the intermediation of brain centers outside the MBH.

Localization and Quantitation of β-Endorphin in Human Brain and Pituitary

The concentration of human β-endorphin (βh-EP) was measured in various hypothalamic nuclei, in extra-hypothalamic brain regions and in the anterior and posterior lobes of the pituitary using a specific radioimmunoassay (RIA). The βh-EP concentrations in the arcuate nucleus (169 ± 35 pg/100 μg protein, n = 7) and median eminence (163 ± 32 pg/100 μg protein, n = 6) were among the highest in the 17 brain areas examined. The immunoreactive βh-EP in the hypothalamus corresponded to authentic βh-EP, as determined by gel exclusion chromatography. By chromatography and RIA the βh-EP concentrations in anterior (1.53 × 105 ±0.51 × 105 pg/100 μg protein, n = 3) and posterior (1.41 × 105 ± 0.38 × 105 pg/100 μg protein, n = 5) pituitary were found to be approximately 1,000-fold higher than in hypothalamus. Within the pituitary βh-EP was localized throughout the anterior lobe, in the pars intermedia and in that part of the posterior lobe nearest the pars intermedia, as judged by immunocytochemistry. Dense immunocytochemical staining was found along the perimeter of many blood vessels. βh-EP and adrenocorticotropin (ACTH) were co-localized in the same pituitary cells. The present data represent the first unequivocal localization and quantitation of βh-EP in human brain and in the separate lobes of the human pituitary.

Effects of maternal smoking on circulating catecholamine levels and fetal heart rates

Eight pregnant chronic cigarette smokers were studied after 34 weeks of gestation to determine the effects of acute cigarette (two nonfilter cigarettes) inhalation on maternal neuroendocrine and cardiovascular changes and on the fetus. Cigarette smoking was found to induce rapid (within 2 1/2 minutes) elevations in maternal plasma norepinephrine and epinephrine levels and this was associated with a rise in maternal pulse and blood pressure. These changes are followed, with a 5 minute lag time, by a significant increase in fetal heart rate. A relatively slow but sustained increase in maternal carboxyhemoglobin (HbCO) concentration occurred. The time course of this increase in HbCO did not seem to be responsible for the acute changes in fetal heart rate. Maternal cortisol levels also showed a slow but sustained elevation. Our present findings, together with data obtained from animal models, suggest that cigarette smoking during pregnancy induces fetal hypoxia through two independent but additive pathways: (1) An acute effect is caused by nicotine activation of adrenergic discharge, resulting in vasoconstriction, a decreased uterine perfusion, and a consequent transient fetal tachycardia, and (2) a delayed but prolonged increase in HbCO may cause a sustained reduction of fetal oxygenation.

An increase in catecholamines and metabolites in the amniotic fluid compartment from middle to late gestation

By means of a modified radioenzymatic assay, simultaneous determinations of the parent catecholamines, epinephrine (E), norepinephrine (NE), and dopamine (DA), and their deaminated metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylglycol (DOPEG), were made in amniotic fluid obtained during the second (N = 44) and third (N = 20) trimesters of normal pregnancies. Significant positive correlations were noted between gestational age and concentrations of E, NE, DA, DOPAC, and DOPEG in amniotic fluid. These findings provide evidence of progressive fetal adrenergic maturation through pregnancy. In addition, our data suggest a parallel maturational event in the central nervous and peripheral catecholamine systems of the fetus, since DOPAC and DOPEG are more representative of catecholamine neuronal activity in the brain.

Reduction by β-endorphin of efflux of dopamine and dopac from superfused medial basal hypothalamus

Abstract The effects of β-endorphin (β-EP) and naloxone on the efflux of dopamine (DA) and its specific deaminated metabolite, dihydroxyphenylacetic acid (DOPAC), from superfused rat medial basal hypothalamus (MBH) were determined. After an equilibration period of 2.5 hrs with Medium 199 at 37°C 0.5 ml fractions were collected. Injection of β-EP, but not medium, into the system significantly reduced (P

Altered Neuroendocrine Status of Middle-Aged Rats Prior to the Onset of Senescent Anovulation

The incidence of senescent anovulation (constant estrus) in female rats increases sharply in the age interval 10--14 months. We have compared the neuroendocrine status of 12-month-old rats, which were still cycling, with that of 6-month-old rats in the reproductive prime. Norepinephrine content in the median eminence of the hypothalamus and circulating levels of FSh and androstenedione were significnatly higher in middle-aged rats (12 months old) than in young controls (6 months old). These increases were selective, in that ten other neuroendocrine parameters measured were unchanged. These results indicate that changes occur at multiple levels of the neuroendocrine system during the transitional phase prior to the onset of senescent anovulation.

Maternal smoking and elevation of catecholamines and metabolites in the amniotic fluid.

To assess the effect of maternal smoking on fetal adrenergic activity, simultaneous measurements in amniotic fluid of the parent catecholamines, dopamine (DA), norepinephrine (NE), and epinephrine (E), as well as the specific intraneuronal deaminated metabolites of DA, 3,4-dihydroxyphenylacetic acid (DOPAC), and of NE, 3,4-dihydroxyphenylglycol (DOPEG), were made by radioenzymatic assay. In the second trimester, a significant (p less than 0.002) and selective elevation of the mean DOPEG concentration was noted in the amniotic fluid of smokers (N = 8) as compared to nonsmokers (N = 36). In the third trimester, significant elevations were found in the mean amniotic fluid concentration of E (p less than 0.0002) and NE (p less than 0.0005), as well as DOPEG (p less than 0.0002), of smokers (n = 12) when compared to nonsmokers (N = 12). There were no significant differences in amniotic fluid concentrations of DA and its deaminated metabolite DOPAC. Since compartmentalization of catecholamines exist between the maternal and fetal circulations, the elevated levels of NE, E, and DOPEG in the amniotic fluid of smokers suggests fetal adrenergic activation as a result of fetal hypoxia and/or by a direct effect of nicotine on the fetal adrenergic system.

Amniotic fluid β-endorphin and α-melanocyte-stimulating hormone immunoreactivity in normal and complicated pregnancies

Abstract β-Endorphin (β-EP) and α-melanocyte-stimulating hormone (α-MSH) are members of a family of peptides which are found in the intermediate lobe of the fetal pituitary gland and placenta. In the present study, concentrations of immunoreactive β-EP (iβ-EP) and α-MSH were determined by radioimmunoassay in the amniotic fluid compartment of both normal (n = 72) and complicated (n = 44) pregnancies. In normal pregnancies, there was a significant (p

Increase of β-endorphin concentrations in the plasma and pituitary neuro-intermediate lobe of the rat on the afternoon of proestrus

Beta-endorphin (beta-EP) concentrations in the plasma and the anterior and neuro-intermediate lobes of the pituitary (AP and NIL) were quantitated by radioimmunoassay (RIA) and gel filtration chromatography in female rats at 1000, 1400, and 1900 h on the day of proestrus and diestrus day-1. There were no significant changes in beta-EP in the plasma, AP, or NIL on diestrus day-1. On proestrus, beta-EP in the plasma and NIL, but not the AP, increased significantly from 1000 to 1400 h and returned to basal levels by 1900 h. The time course of this increase of beta-EP in the NIL and plasma is consistent with the temporal sequence of the prolactin and gonadotropin surges on the afternoon of proestrus, suggesting that beta-EP in the NIL may be involved in the regulation of these neuroendocrine events.

Attenuation during Aging of the Postovariectomy Rise in Median Eminence Catecholamines

The effects of aging on the responsiveness of the neuroendocrine system to ovariectomy and estrogen replacement were determined. Neuroendocrine responsiveness in young (6-month-old) cyclic rats was compared to that in old (24-month-old) constant estrous rats. Seven neuroendocrine parameters were examined: median eminence (ME) concentrations of norepinephrine (NE), dopamine (DA) and luteinizing hormone-releasing factor (LRF) and circulating concentrations of LH, FSH, prolactin (PRL) and 17 beta-estradiol (E2). These concentrations were measured in intact and ovariectomized rats and in ovariectomized rats treated for 3 weeks with E2. 3 weeks after ovariectomy of young rats the ME concentrations of NE (38.0 +/- 10.4 pg/microgram, n = 15) and DA (201 +/- 32 pg/microgram, n = 15) were significantly higher (p less than 0.05) than the respective levels in intact proestrous controls (18.7 +/- 1.9 pg/microgram, n = 18) and 89.4 +/- 12.4 pg/microgram, n = 18). In old rats there was no significant change in ME concentration of NE after ovariectomy. ME DA levels in old rats did rise after castration by 62%; however, this rise was only half of that in young animals (125%). The increases in DA after ovariectomy could be completely reversed by E2 in both young and old rats. ME concentration of LRF was reduced after castration to a similar extent in young (76%) and old (81%) rats, and these effects were partially E2-reversible in both age groups. The postovariectomy increases in LH (485%) and FSH (665%) in young rats were greater than the respective increases in old rats (169) and 191%). In contrast, the changes in PRL concentration following ovariectomy and E2 replacement were similar in magnitude in both age groups. The present results indicate that the neuroendocrine responsiveness to ovariectomy is altered during aging. This alteration in responsiveness is selective, in that changes were demonstrable in only 2 out of 7 parameters measured.