Biomedical subjects
Publications and source records attributed to D P Cardinali.
Tubulin levels of the medial basal hypothalamus (MBH) were greater in male than in female rats. Orchidectomy brought about a decrease of MBH tubulin concentration, whereas testosterone injection augmented it in the MBH and adenohypophysis. Estradiol administration augmented MBH tubulin and protein concentration.
The effects of FSH and LH on norepinephrine (NE) turnover in pineal gland and superior cervical ganglia of castrated female rats were examined by measuring the decline of [3H]NE concentration in the organ 30--120 min after a single i.v. injection of the labeled amine. Both FSH and LH treatment significantly decreased [3H]NE turnover in the pineal gland whereas only FSH accelerated it in the ganglia. As compared to controls, the initial uptake of [3H]NE was lower in the pineal gland of FSH- and LH-treated animals, and higher in the superior cervical ganglia of rats injected with FSH. Neither FSH nor LH modified [3H]NE turnover in heart or adrenal gland, nor changed their endogenous catecholamine content. Pineal monoamine oxidase (MAO) activity type B (assaying by using beta-phenylethylamine as substrate) was decreased by FSH or LH injection. Only FSH modified MAO activity in the ganglia by increasing significantly type A enzyme (assaying by using serotonin as substrate). These results suggest that FSH and LH affect significantly NE metabolism in pineal gland and superior cervical ganglia of spayed rats.
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Incubated bovine pineal glands released prostaglandin E-and prostglandin F-like material (304 +/- 20 and 582 +/- 56 pg/mg dry tissue wt/h, respectively) and the release was increased 2.2 2.9-fold by adding 10(-4)-10(-6)M of norepinephrine to the medium. Binding assays revealed the existence of high affinity binding of 3H-prostaglandin E2 (3H-PGE2) and 3H-prostaglandin F1 alpha (3H-PGF2 alpha) in low speed supernatants of pineal homogenates. Binding was increased by increasing Ca++ concentration in medium up to 2 mM, was heat labile and was depressed following incubation with trypsin. In subcellular fractionation studies maximal 3H-PG binding was found in the 27000 x g pellet. Scatchard analysis of 3H-PGE2 binding revealed the presence of a single population of binding sites with a Kd= 1.2 nM and a binding site concentration of 1-2 pmoles/g protein. A single population of binding sites for 3H-PGF2 alpha was also detected with a Kd= 1.7 nM and a similar binding site concentration. Non-radioactive PGE1 and PGE2 were almost equally effective to compete for 3H-PGE1 binding sites (ED50= 5 and 2 nM, respectively). Unlabeled PGF1 was relatively ineffective to compete for 3H-PGE2 binding (ED50 greater than 1000 nM) but displaced effectively 3H-PGF2 alpha binding (ED20=1.2 nM).
The effect of pineal indoles on fast axoplasmic transport of proteins in the sciatic nerve was examined in rats injected with [3H]leucine in the sixth lumbar dorsal root ganglion. Melatonin (350-1100 nmol) applied locally in the sciatic nerve impaired significantly axonal transport. At a 350-nmol dose all other indoles tested (i.e., 5-hydroxyindoleacetic acid, 5-methoxyindoleacetic acid, serotonin, N-acetylserotonin, tryptamine, 5-methoxytryptamine) were less potent than melatonin to impair fast axonal flow. Vinblastine injected either into the ganglion or in the sciatic nerve markedly inhibited axonal transport.
A diurnal variation in neuroendocrine sensitivity to melatonin is known to occur in hamsters and rats. The present experiments were carried out to examine the possibility that affinity and/or number of melatonin binding sites in brain could change accordingly at the two times when exogenous melatonin is known to be ineffective or effective to produce neuroendocrine changes, i.e., at 07 : 00 or 20 : 00 h (lights on from 07 : 00 to 21 : 00 h daily). The number of melatonin binding sites in hamster and rat brains was at 20 : 00 h 34--56% higher than at 07 : 00 h, without changing their affinity towards [3H]melatonin (hamster: Kd = 53 nM; rat: Kd = 73--77 nM). These alterations in melatonin receptor density may play a role in daily changes in sensitivity to the exogenous methoxyindole.
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The possible existence of pineal progesterone (P) receptors was assessed in 105,000 g supernatants of bovine pineal glands incubated with 3H-P in the presence of 10 microM cortisol. By charcoal adsorption analysis specific binding (defined as the difference between 3H-P binding in the absence and presence of 1,000-fold excess of unlabeled P) attained its maximum after 60 min at 37 degrees C. Binding was abolished by heating the cytosol or by preincubating it with trypsin. A single population of binding sites with a Kd = 1.64 nM and binding site concentration = 34 fmol/mg of cytosol protein was detectable by Scatchard analysis. In competition experiments the B50 progesterone values (nM) were: P (2), 20 alpha-dihydroprogesterone (12), 20 beta-dihydroprogesterone (25), estradiol (158), testosterone (675) and corticosterone (greater than 1,000). After sucrose gradient centrifugation of pineal cytosol incubated with 3H-P a discrete peak of radioactivity in the 7-8 S region of the gradient was observed, and disappeared following incubation with excess unlabeled P. These results indicate that P receptors are present in the bovine pineal gland.
The effect of melatonin on luteinizing hormone (LH) relase was studied in castrated female rats injected with estradiol and progesterone. Melatonin administered s.c. twice daily for 6 days exerted a biphasic, dose-related effect on LH release, the lowest dose (125 micrograms/100 g body weight) being stimulatory and the highest (250 micrograms/100 g body weight) inhibitory. Superior cervical ganglionectomy negated the inhibitory effect of the high metatonin dose on steroid-induced LH release. Rather melatonin injection to ganglionectomized rats resulted in significantly higher serum LH values than those of animals injected with estradiol and progesterone alone. Melatonin treatment failed to modify postcastration serum LH levels.
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The effects of melatonin on serum prolactin levels were examined in ovariectomized rats primed with oestradiol and progesterone, and subjected to bilateral superior cervical ganglionectomy or pinealectomy. Ganglionectomy resulted in a significant depression of the serum prolactin concentrations, as well as in impairment of the prolactin release evoked by administration of steroid. Treatment with melatonin increased serum prolactin in control but not in ganglionectomized rats. Injection of melatonin protentiated the steroid-induced release of prolactin in control rats; this effect of melatonin was not detected in ganglionectomized rats. Pinealectomy did not affect basal prolactin levels, nor impair the release of prolactin evoked by steroid treatment; however, it was effective in blocking the melatonin-induced release of prolactin in vehicle-treated rats, as well as the potentiation of steroid-induced prolactin release by melatonin. Intracranial surgery by itself increased prolactin release. These results suggest that systemically administered melatonin needs an intact pineal gland to augment serum prolactin levels.
This article discusses the experimental evidence which suggests that the pineal gland and its innervating neurons are useful paradigms for the study of neuroendocrine integrative processes. The obtained results can be summarized as follows: 1) existence of putative receptors for various hormones (estradiol, testosterone, 5 alpha-dihydrotestosterone, progesterone, prolactin) in the mammalian pineal gland; (2) steroid metabolic pattern in the pineal gland resembling other brain areas involved in gonadotrophic regulation; (3) control of pineal estrophilic and androphilic receptors by adrenergic transmitter through beta-adrenergic receptors and at a translational level; (4) denervation supersensitivity of hormone receptors to neurotransmitter; (5) modification of neuronal activity by hormone treatment at ganglionic and preganglionic sites of action; (6) estrophilic binding sites in ganglia; (7) correlation of pineal responsiveness to hormones with activity of sympathetic nerves; (8) modification by hormones of pineal beta-adrenergic mechanisms; (9) dissociation of hormone effects on the pineal gland in those mediated or modulated by changes in afferent neuronal activity and those relatively unaffected by denervation. Collectively these data indicate that neuroendocrine, endocrine-neural and endocrine-endocrine transducing processes occur in the pinealocytes and superior cervical ganglia.
In the brain of rats injected with pentoxifylline [3,7-dimethyl-1(5-oxo-hexyl)-xanthine] or aminophylline the following was observed: (i) dose-dependent increases of tryptophan and 5-hydroxyindoleacetic acid levels and of 5-hydroxytryptophan and dihydroxyphenylalanine accumulation after treatment with the decarboxylase inhibitor benserazide HCl; (ii) acceleration of norepinephrine turnover following alpha-methyl-p-tyrosine; (iii) increase of 3-methoxytyramine accumulation following pargyline. On a molar basis pentoxifylline was more potent than aminophylline in affecting brain biogenic amine metabolism.
Pineal protein synthesis in female rats, estimated from the incorporation of labeled amino acids into proteins in vitro, exhibited significant changes as a function of the stage of the estrous cycle. These changes were restricted to the proestrous and estrous days; pineal protein synthesis attained its maximum on the morning of proestrus declining abruptly by 53% during the evening, at the time of the expected gonadotrophin and prolactin release. Pineal serotonin-N-acetyltransferase activity increased by 10 to 15 times during night-time on every day of cycle; no appreciable modification of its daily rhythm was detected along the estrous cycle. Spayed rats treated for 2 days with progesterone showed a dose-dependent decrease of amino acid incorporation into pineal proteins, regardless of whether estradiol was simultaneously administered or not. Pineal protein synthesis in spayed rats administered with estradiol for 2 days and killed at 11 a.m. and 5 p.m. on the third day, did not show differences as a function of time of sacrifice. When progesterone was injected on the morning of the third day a significant decline in protein synthesis was observed at 5 p.m. Only in the latter group serum LH levels showed significantly greater values at 5 p.m. Pineal serotonin content of estradiol-treated rats increased significantly at evening, an effect which was obliterated by the administration of progesterone; progesterone alone did not affect pineal serotonin content. Radioactivity uptake by pineal glands incubated with labeled progesterone did not show changes along the estrous cycle. These data argue in favour of the involvement of progesterone in the changes of pineal protein synthesis observed during the "critical period" for gonadotrophin and prolactin release.
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Secretions from the pineal gland participate in the control of reproductive function. In turn gonadal steroids, gonadotrophins and prolactin modify pineal metabolic activity and change the rate of synthesis of pineal hormones. The article reviews the major observations made regarding the pineal gland and its innervating neurons as target tissues for reproductive steroid and hypophyseal hormones.
The effect of estradiol and testosterone on the activity of catechol-O- methyl transferase (COMT) of the superior cervical ganglion, pineal gland, anterior hypophysis and hypothalamus were examined in castrated rats. In female rats a single injection of 2 mug of estradiol caused a significant 25% increase of hypothalamic COMT, whereas after 3 daily injections no differences in enzyme activity were observed between hormone- and vehicle-injected controls. In male rats testosterone propionate (0.5 mg) increased hypothalamic COMT by 53%; this effect was not detectable in animals treated with the androgen for 3 days. COMT activity of the superior cervical ganglion, pineal gland and anterior hypophysis did not exhibit significant changes after any of the hormone schedules used.
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