Jorge M. Rosner

Effects of melatonin on neurotransmitter uptake and release by synaptosome-rich homogenates of the rat hypothalamus.

Preincubation of synaptosome-rich homogenates of rat hypothalamus with melatonin resulted in significant decreases of norepinephrine, serotonin, dopamine and glutamate uptake. Melatonin inhibition was noncompetitive; apparent Kms of initial uptake processes were: (2.5 +/- 0.3) x 10(-7) M for norepinephrine, (2.6 +/- 0.3) x 10(-7) M for serotonin, (2.4 +/- 0.4) x 10(-7) M for dopamine and (1.0 +/- 0.3) x 10(-7) M for glutamate. Apparent Kis for melatonin inhibition of transmitter uptake were: 0.64 +/- 0.14 mM (norepinephrine), 0.23 +/- mM (serotonin), 0.51 +/- 0.08 mM (dopamine) and 1.21 +/- 0.10 mM (glutamate). Transmitter release evoked by increasing [K+] in medium to 30 mM was augmented by melatonin in a dose-dependent manner. Maximal effects were observed on serotonin release. Accumulation of 3H-melatonin within synaptosome-rich homogenates did not exhibit differences between 0 and 37 degrees C, indicating that the uptake of the hormone was not an active process. These results suggest that exogenously-administered melatonin may affect neurotransmitter accumulation and release in the hypothalamus by modification of the transmitter uptake mechanism rather than by competition with the transmitter for its uptake pump.

Control of estrogen and androgen receptors in the rat pineal gland by catecholamine transmitter

Abstract Sucrose gradient studies of rat pineal cytosol incubated with 3 H-estradiol (female pineals) or 3 H-5 α -dihydrotestosterone (male pineals) revealed a radioactivity peak in the 8 S region which disappeared after superior cervical ganglionectomy or incubation with excess unlabeled hormone. Ganglionectomy decreased significantly estradiol and testosterone uptake by the pineal gland in vitro as well as high affinity binding to pineal cytoplasmic and nuclear components. Norepinephrine treatment counteracted all the effects of ganglionectomy but was unable to modify hormone uptake and binding by the pineal gland of sham-operated controls. Pre-treatment with actinomycin D or propranolol but not with phentolamine impaired norepinephrine effects; propranolol blockage however was only partial. Administration of isoproterenol, L-dopa or phentolamine increased hormone uptake by denervated pineals. The effects of isoproterenol were also observed in vitro and were blocked by propranolol. These results indicate that sex steroid receptors in the pinealocytes are controlled by norepinephrine via beta-adrenergic receptors and that depletion of neural norepinephrine enhanced responsiveness of pineal hormone receptors to exogenous catecholamines.

Effects of estradiol on melatonin and protein synthesis in the rat pineal organ.

The effects of estradiol on pineal function haveinsofar been studied by administering supramaximal, non-physiological doses of the hormone. The present experiments were undertaken to assess estradiol-

Gonadal steroids as modulators of the function of the pineal gland

Sex steroids affect pineal function. Castration or the administration of estradiol, testosterone, or progesterone bring about changes in pineal melatonin synthesis, as well as in other aspects of pineal activity in rats. This paper deals with some of the mechanisms underlying steroid action on pineal metabolism. Estradiol is avidly taken up in vivo and in vitro by the pineal gland. A cytosol binding protein having a Kd of, (0.27 ± 0.08) × 10−9M for estradiol and requiring SH groups for full expression of binding activity was detected in pineal homogenates. Estradiol uptake by the pineal and the uterus of mature rats attained their minima on the day of proestrus. A priming dose of estradiol increased high affinity binding sites for estradiol in pineal and uterine cytosol by about 150%. Testosterone is also readily taken up and retained in vivo and in vitro by the pineal of orchiectomized rats. Saturation kinetics analysis of androgen binding to bovine pineal cytosol indicated a Kd of 1.57 × 10−9M for testosterone and 0.36 × 10−9M for 5α-dihydrotestosterone. The cytoplasmic binder was shown to be a protein and to require SH groups for binding activity. Testosterone was metabolized by the pinealocytes into 5α-dihydrotestosterone, 5α-androstanediol, androstenedione and 5α-androstanedione; 5α-dihydrotestosterone was the major metabolite in the nuclei of pineal cells. Superior cervical ganglionectomy or exposure of rats to light increased androstenedione synthesis, whereas ganglionectomy or exposure to darkness decrease 5α-androstanedione synthesis. Progesterone is taken up by the pinealocytes in vitro up to a tissue concentration 18-fold that of the media. [3H]Progesterone is converted in the pinealocytes into 5α-pregnanedione and 3α-hydroxy-5α-pregnan-20-one. These data suggest that the early steps of sex steroid action on pineal cells resemble those of steroid target tissues.

Effects of Castration and Testosterone Administration on Pineal and Retinal Hydroxyindole-O-Methyl Transferases of Male Rats

The effects of castration andtestosterone treatment on pineal and retinal hydroxyindole-O-methyl transferases (HIOMT) were investigated in male rats. Pineal and retinal HIOMT activities decreased 24–7

Plasma testosterone and serum lipids in male survivors of myocardial infarction.

The concentration of blood testosterone and its correlations with plasma lipids were studied in 23 middle aged survivors of myocardial infarction. They had significantly higher mean cholesterol, triglycerides and total lipids than controls. Plasma triglycerides were highest in five patients who showed the lowest plasma testosterone values. The mean plasma testosterone was significantly lower (P < 0.001) in the myocardial infarction patients (ovbar|X: 4360.3; S.E.: 584.9pg/ml) than in control group of similar ages (X: 6880.4; S.E.: 484.9pg/ml). Many of these patients, although fully recovered, seemed to have a reduced testosterone secretion.

Effects of melatonin, serotonin and n-acetylserotonin on the production of steroids by duck testicular homogenates

A progonadal function of the pineal gland has been previously established in the duck and in order to determine whether melatonin has a direct effect on the “in vitro” production of steroids by the duck testis the following experiments were performed. Duck testicular homogenates were incubated with labeled progesterone, androst-4-en-3, 17-dione and 3β-hydroxyandrost-5-en-17-one. Progesterone-4-14C was converted to 17α-hydroxypregn-4-en-3, 20-dione, androst-4-en-3, 17-dione, testosterone, 20α-hydroxypregn-4-en-3-one, 17α, 20α-dihydroxypregn-4-en-3-one, 6β-hydroxypregn-4-en-3, 20-dione, 5α-pregnane-3, 20-dione and 5α-androstane-3, 17-dione. Androst-4-en-3, 17-dione-4-14C was metabolized to testosterone and 5α-androstane-3, 17-dione while 3β-hydroxyandrost-5-en-17-one-4-14C was converted to androst-4-en-3, 17-dione, testosterone and 5α-androstane-3, 17-dione. Melatonin (2 m μ moles/ml of incubation medium) inhibited the activity of the 3β-hydroxysteroid dehydrogenase-4-5-ene isomerase system, 17α-hydroxylase, 6β-hydr oxylase and 5α-, 17β(C19 steroid)-and 20α-reductase. No effects of serotonin and N-acetylserotonin were observed when doses below 200 m μ moles/ml were utilized. Although the pineal gland has a progonadal function in the duck, a specific inhibitory effect of melatonin on the testicular production of steroids could be demonstrated.

Testosterone effects on protein synthesis in the rat pineal gland. Modulation by the sympathetic nervous system

Abstract The administration of 0.5 mg of testosterone propionate (TP) for 3 days to castrated male rats caused 3H-leucine incorporation into pineal proteins to increase significantly by 79%. TP effects depended on time of administration; rats receiving TP at 06.00 h exhibited a significant 150% increase in pineal protein synthesis 24 h later whereas rats injected at 14.00 h only showed a 54% increase in 3H-leucine incorporation into proteins. Superior cervical ganglionectomy decreased pineal testosterone uptake in vitro by 21% and pineal protein synthesis by 27%; in addition it blocked the stimulatory effects of TP on protein synthesis. Ganglionectomy also modified the in vitro metabolism of testosterone by pineal cells; it increased the amounts of 3H-androstenedione and decreased 3H-5∝-androstanedione extracted from pineal glands incubated with 3H-testosterone. These results indicate that the sympathetic nervous input reaching the pineal via the superior cervical ganglia is important to modulate the early steps of androgen action on the pinealocytes.

Rat Brain Norepinephrine Release During Progesterone-Induced LH Secretion

The administration of 1.5 mg of progesterone to ovariectomized estrogen-primed rats induced a surge in plasma norepinephrine (NE) preceding the pituitary LH release. The injection of reserpine (2 mg/kg) 2 h prior to progesterone completely blocked the progesterone effects on both NE and LH plasma surges. On the other hand, the adminitration of phenoxybenzamine prior to progesterone, blocked the steroid effect on LH without inhibiting the plasma NE rise. Contrarily, the alpha-blocker was able to induce a rapid increase in the amine levels 2 h after its injection. The determination of NE in the anterior hypothalamus of these rats revealed that simultaneously with the plasma NE rise induced by progesterone there was a fall in the hypothalamic amine levels. Both reserpine and phenoxybenzamine caused a depletion in the amine content of the anterior hypothalamus. In experiments measuring the arteriovenous difference in the concentration of NE across the brain following progesterone-induced LH release, it was found that most NE comes from the brain. The amine rise was evident in the jugular vein while the arterial NE concentration showed a slight increase. These findings raise the possibility that the changes in circulating NE may reflect an enhanced noradrenergic activity occurring in the brain from which the LH surge results.

Uptake and effect of 17β-estradiol on pineal hydroxy-indole-o-methyl transferase (HIOMT) activity

In the present work we have studied a) the uptake of estradiol by the pineal gland and b) the effects of exogenous estradiol and norepinephrine on pineal hydroxy-indole-O-methyl transferase (HIOMT) activity. The uptake of estradiol by the pineal gland, the uterus and the cerebral cortex of castrated rats was determined 15–240 min after the intraperitoneal administration of a single dose of [6,7−3H] 17β-estradiol. The pineal took up and retained significantly more [3H] estradiol per mg of tissue than either the uterus or the cerebral cortex (p<0.01). The simultaneous injection of norepinephrine plus labeled estradiol did not modify significantly the estradiol uptake by the pineal gland. Estradiol administration for 3 days decreased pineal HIOMT activity (p<0.01), this effect being reversed by the simultaneous injection of norepinephrine. When norepinephrine was injected alone, no effects on pineal HIOMT were observed. These results suggest the existence of an estradiol receptor system in the rat pineal gland.