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Biomedical subjects

C Santana

Publications and source records attributed to C Santana.

At least 55 records · Page 3Linked to original sources
PubMed1989

Role of postsynaptic alpha-adrenergic receptors in the beta-adrenergic stimulation of melatonin production in the Syrian hamster pineal gland in organ culture.

The role played by postsynaptic alpha-adrenergic receptors in the stimulation of pineal melatonin production was investigated in the Syrian hamster. The studies were conducted using organ cultured pineal glands collected from both anatomically intact and superior cervical ganglionectomized hamsters. Results obtained indicate that phenylephrine, an alpha-adrenergic agonist, by itself has no effect in promoting melatonin production; however, it potentiates the stimulatory effects of isoproterenol, a beta-adrenergic agonist, on pineal melatonin production in nonoperated hamsters. Similar observations were obtained with pineal glands whose presynaptic terminals were removed by prior superior cervical ganglionectomy. However, a longer incubation time was required (4-6 hours vs. 2 hours) with pineal glands taken from ganglionectomized animals. Apparently, beta-adrenergic activation is an absolute requirement to stimulate pineal melatonin production, and an alpha-adrenergic receptor mechanism potentiates beta-adrenergic activation. In addition, the findings obtained with denervated pineal glands suggest that the regulation of pineal melatonin production by both alpha- and beta-adrenergic mechanisms is through receptors located on postsynaptic structures.

Animals↗
PubMed1989

Nocturnal increase of type II thyroxine 5'-deiodinase activity in the Syrian hamster harderian gland is abolished by light exposure and induced by isoproterenol.

The presence of type II 5'-deiodinase activity in the Syrian hamster Harderian gland was investigated. This enzyme exhibited an increase of its activity after animals entered the normal dark phase, with maximal activity occurring at 04.00 hr (8 hr after lights off). The nocturnal increase was prevented by maintaining the animals in light during the night. Isoproterenol subcutaneously injected every 2 hr (1.0 mg/kg body wt) from 20.00 hr through 0.400 hr to animals exposed to light during the normal dark period mimicked the effect of darkness, i.e., with this treatment an increase in 5'-deiodinase activity with maximal peak values at 02.00 hr was observed. The results show that 5'-deiodinase activity in the Syrian hamster Harderian gland exhibits a nyctohemeral profile dependent on beta-adrenergic activation of the gland.

Animals↗
PubMed1989

Testosterone increases N-acetyltransferase activity in both male and female Syrian hamster harderian glands.

N-acetyltransferase (NAT) activity was studied in the Harderian glands of intact and castrated (with or without subcutaneous testosterone implants) male and female Syrian hamsters. Castration in male hamsters produced a significant drop in the NAT activity. Castrated males with testosterone implants had NAT activity levels comparable to those in intact males. Ovariectomy did not modify NAT activity. Ovariectomized hamsters with testosterone implants exhibited a significant increase in the Harderian NAT activity reaching the same values as those in the glands of the male hamsters.

Acetyltransferases↗
PubMed1988

The in vitro activation of cyclic AMP production by either forskolin or isoproterenol in the Syrian hamster pineal during the day is not accompanied by an increase in melatonin production.

The role of cyclic AMP in the regulation of melatonin production was investigated in cultured Syrian hamster pineal glands. Forskolin markedly increased cyclic AMP production in pineal glands collected either late in the light period or in the dark period. The effect of forskolin was synergistically enhanced by 3-isobutylmethylxanthine, a phosphodiesterase inhibitor; however, increase in cyclic AMP after isoproterenol was only apparent in the presence of 3-isobutylmethylxanthine. Since beta-adrenergic agonists are able to stimulate melatonin production late in the dark period only, these data suggest that, in the hamster pineal gland, there may be intracellular mechanisms in addition to a cyclic AMP increase required for induction of melatonin production by beta-adrenergic agonists.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Beta-adrenergic stimulation prior to darkness advances the nocturnal increase of Syrian hamster pineal melatonin synthesis.

Pineal glands of male Syrian hamsters stimulated in vivo with isoproterenol (ISO) for 4 h before the onset of darkness showed a 4-h advance in the timing of the nighttime increases in both N-acetyltransferase activity and melatonin levels. When ISO (1 mg/kg) was administered every 2 h to animals kept in light during the night, a significant increase in melatonin synthesis was observed after 4-6 h. The results suggest that the Syrian hamster pineal gland can respond in vivo to continuous beta-adrenergic stimulation, but a lag period of 4-6 h is required before there is an increase in melatonin synthesis.

Animals↗
PubMed1988

Forskolin, an activator of adenylate cyclase activity, promotes large increases in N-acetyl transferase activity and melatonin production in the Syrian hamster pineal gland only during the late dark period.

The exposure of organ cultured pineal glands of Syrian hamsters to forskolin, an adenylate cyclase activator, caused marked increases in serotonin N-acetyltransferase activity and melatonin content in a dose-related manner (1-100 microM) when glands were collected in the second half of the dark period. However, addition of forskolin to glands collected anytime during the light period or at the beginning of the dark period failed or only modestly stimulated either pineal N-acetyltransferase activity or melatonin levels. Similar results were obtained with isoproterenol. The results suggest that intrapinealocyte regulatory mechanisms may determine the nocturnal rise in the Syrian hamster pineal gland.

Acetyltransferases↗
PubMed1988

Effect of isoproterenol and dibutyryl cyclic AMP on thyroxine type-II 5'-deiodinase and N-acetyltransferase activities in rat pineal organ cultures.

The effects of either isoproterenol or dibutyryl cyclic AMP on rat pineal thyroxine type-II 5'-deiodinase (5'-D) and N-acetyltransferase (NAT) activities were studied using an organ culture technique. Moving the animals to light at night dramatically inhibited the NAT with no change in the 5'-D activity. The subsequent incubation of pineal glands with either isoproterenol or dibutyryl cyclic AMP restored the NAT activity and caused a further rise in 5'-D activity. In animals maintained under light conditions during the night, both isoproterenol and dibutyryl cyclic AMP were able to stimulate the 5'-D and NAT activities. The results suggest that the beta-adrenergic activation of the 5'-D activity is mediated by cyclic AMP in the rat pineal gland.

Acetyltransferases↗
PubMed1988

Differential responses of rat pineal thyroxine type II 5'-deiodinase and N-acetyltransferase activities to either light exposure, isoproterenol, phenylephrine, or propranolol.

1. Compared to pineal N-acetyl transferase (NAT) activity, which exhibited a dramatic drop following acute light exposure at night, nocturnal rat pineal thyroxine type II 5'-deiodinase (5'-D) activity was minimally influenced by the same light exposure. The injection of cycloheximide, a potent inhibitor of protein synthesis, although it did curtail the rise in NAT activity for at least 2 hr, did not elicit decreases in the activities of either 5'-D or NAT enzymes. Propranolol, a beta-adrenergic blocker, either delayed the continued nocturnal rise in 5'-D activity when injected at 0000 hr or slightly enhanced the fall in 5'-D activity when injected at 0200 hr. These results suggest that interruption of the synthesis of proteins is responsible for the slow deterioration of 5'-D activity induced by either light or propranolol. 2. The slight fall in 5'-D activity induced by light at night was prevented by isoproterenol; phenylephrine, however, did not prevent the fall and the effect of isoproterenol + phenylephrine was similar to that obtained with isoproterenol alone. On the other hand, the light-inhibited NAT activity recovered after the injection of isoproterenol; phenylephrine did not elicit any effect, but the injection of both isoproterenol and phenylephrine simultaneously caused a greater NAT response than that induced by isoproterenol alone. 3. When injected during the day, phenylephrine had no effect on either pineal 5'-D or NAT activities; however, the injection of either isoproterenol alone or isoproterenol + phenylephrine elicited 5-fold and 10-fold increases in nocturnal, light-suppressed 5'-D and NAT activities, respectively. During the day, phenylephrine did not potentiate the effects of isoproterenol on NAT activity as it did at night. When the effects of isoproterenol on the 5'-D activity were compared to rats exposed to light during the day and at night, the activity of 5'-D reached a higher level at night than during the day.

Animals↗
PubMed1988

Darkness-induced changes in noradrenergic input determine the 24 hour variation in beta-adrenergic receptor density in the rat pineal gland: in vivo physiological and pharmacological evidence.

In male rats housed under a 14:10 LD cycle (lights on at 0600 h), pineal beta-adrenergic receptors, assessed as 125Iodopindolol (IPIN) binding to membrane preparations, showed a 24 hour variation characterized by a nocturnal increase that peaked around middark (2300 h-0200 h) and a decrease during the latter half of the dark period. Animals exposed to light for 3 hours into the normal dark period showed a similar increase in IPIN binding that was prevented by a single sc injection (0.5 mg/kg) of isoproterenol (ISO). The decrease in IPIN binding observed after middark was prevented both by moving the animals to light at 0200 h and by propranolol administration (20 mg/kg). Likewise, the reduction in IPIN binding was induced in light exposed animals both by ISO administration (in a dose dependent manner) and by injection of norepinephrine (NE) plus the catecholamine uptake blocker desmethylimipramine (DMI). DMI alone was without effect. Chronic denervation of the pineal gland by superior cervical ganglionectomy (SCGx) increased IPIN binding to levels not higher than those observed at middark. The results suggest that rat pineal beta-adrenergic receptors are regulated in a rhythmic 24 hour pattern. A decrease in density (downregulation) induced by a darkness-associated increase in NE release, occurs late in the night before lights on; recovery from the down regulated state (upregulation) occurs during the light and early dark phase, reaching a maximum density of beta-adrenergic receptors at middark not different from that observed in chronically denervated pineal glands.

Animals↗
PubMed1988

Effects of photoperiod or exogenous melatonin administration on the activity of N-acetyltransferase and hydroxyindole-O-methyltransferase and the melatonin content of the harderian gland of two strains of female Syrian hamsters.

The activities of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) and the melatonin concentration of the Harderian glands of two strains of Syrian hamster females (outbred and inbred LSH/SsLak) exposed to two different photoperiods (14:10 h and 8:16 h) were studied. The Harderian glands of the inbred hamsters showed greater NAT activity than those of the outbred animals. On the other hand, the glands of the outbred hamsters exhibited higher HIOMT activity and melatonin content than those of the inbred LSH/SsLak. Short photoperiod exposure, which produced gonadal regression in the inbred but not in the outbred hamsters, decreased the NAT activity in the inbred animals to the levels of the outbred. HIOMT activity was not affected by the lighting conditions. After the exposure to short days, the melatonin content of the inbred hamster Harderian glands increased to that in the outbred animals. Daily melatonin injections, which caused gonadal regression in the LSH/SsLak but not in the outbred hamsters, did not stimulate the effect of the short photoperiod on the Harderian gland NAT activity and melatonin content of the inbred hamsters.

Acetylserotonin O-Methyltransferase↗
PubMed1988

Inhibition of pineal type-II 5'-deiodinase does not affect the nocturnal increase of N-acetyltransferase activity and melatonin content in either euthyroid or thyroidectomized rats.

The presence of type-II thyroxine 5'-deiodinase (5'-D) activity in rat pineal gland has been previously described. In the present paper, 5'-D activity, N-acetyltransferase (NAT) activity, and melatonin content were measured in the same rat pineal. Each of these constituents exhibits a nocturnal increase with peak values at 0100 h for melatonin (1.20 +/- 0.12 ng/gland) and at 0300 h for both 5'-D (39.5 +/- 11.9 fmol/gland/h) and NAT (8.38 +/- 1.04 nmol/gland/h) activities. In vivo treatment with iopanoic acid (IOP) completely prevented the nocturnal increase in 5'-D activity (14.1 +/- 2.6 fmol/gland/h at 0300 h) with no modification in either the NAT activity or melatonin content. Thyroidectomy greatly enhanced the 5'-D activity during the dark period (102.9 +/- 10.2 vs. 31.6 +/- 4.2 fmol/gland/h), reaching a peak at 0200 h; thyroidectomy, however, did not affect daytime pineal 5'-D activity (3.11 +/- 0.78 vs. 2.5 + 0.92 fmol/gland/h). Treatment of rats with IOP acid completely inhibited the pineal 5'-D activity in both control (7.86 +/- 0.88 fmol/gland/h) and thyroidectomized animals (2.24 +/- 1.10 fmol/gland/h) with no change in the melatonin content of the gland (1.21 +/- 0.32 vs. 0.99 +/- 0.18 ng/gland).

Acetyltransferases↗
PubMed1988

Stimulatory effect of isoproterenol but not of dibutyryl cyclic AMP on N-acetyltransferase activity and melatonin content of Syrian hamster pineal gland in organ culture.

The purpose of this study was to compare the response of Syrian hamster pineal glands in organ culture either to isoproterenol, a beta-adrenergic agonist, or to dibutyryl cyclic AMP. When pineal glands were collected at night, hamsters were exposed to light for 30 min to depress pineal N-acetyltransferase (NAT) activity and melatonin values to low levels. Pineal glands were removed and placed in organ culture containing either isoproterenol or dibutyryl cyclic AMP and subsequent changes in NAT activity and melatonin levels were measured. At night, isoproterenol (10(-7) or 10(-6) M) induced an increase in the NAT activity and melatonin levels in both pineals and culture media. However, dibutyryl cyclic AMP was either ineffective or minimally effective in stimulating these parameters at either different incubation times (2, 4, and 6 h) or drug concentrations (0.1, 0.5, and 1.0 mM). Conversely, when rat pineal glands were incubated with either isoproterenol (10(-7)) or dibutyryl cyclic AMP (0.5 mM) dramatic rises in NAT activity and melatonin levels were observed. In another experiment, hamster pineal glands were collected from animals killed either late in the light period (19.00 h) or in the latter half of the dark period. Isoproterenol promoted NAT activity and melatonin production only in glands collected in the latter half of the dark phase.

Acetyltransferases↗
PubMed1988

Thyroxine 5'-deiodination in brown adipose tissue and pineal gland: implications for thermogenic regulation and role of melatonin.

T4 type II 5'-deiodinase (5'-D II) activity was studied in wild-captured Richardson's ground squirrels. As previously reported for other species, 5'-D II activity was detected in frontal cortex, cerebellum, pineal gland, and brown adipose tissue (BAT); in the median eminence the levels of 5'-D II activity were undetectable with our methodology. When pineal gland, frontal cortex, and cerebellum nyctohemeral profiles were studied, none of them showed variations. Cold exposure for 4 h led to an increase in the enzymatic activity 10-fold above the basal values for BAT, while in the pineal gland the values were doubled; cold exposure failed to change the 5'-D II activity in the frontal cortex. Acute melatonin treatment caused a 7-fold increase in 5'-D II activity in BAT, but did not affect enzyme activity in either the pineal gland or frontal cortex. The data indicate that 5'-D II in Richardson's ground squirrel shows classical localizations. Additionally, two new regulatory factors of 5'-D II are reported, i.e. melatonin for BAT and cold for the pineal gland.

Adipose Tissue, Brown↗
PubMed1988

Androgenic control of immunoreactive somatostatin in the Harderian gland of the Syrian hamster.

Harderian glands of Syrian hamsters contained measurable levels of immunoreactive somatostatin. After an extraction procedure, serial dilutions of tissue were assayed and showed parallelism in the displacement curve with dilutions of purified somatostatin standard in the radioimmunoassay. Somatostatin concentrations were higher in female hamsters (10.0 +/- 2.1 ng/mg protein) than in males (2.6 +/- 0.4 ng/mg protein). Castrated males had somatostatin values in the range of females (12.4 +/- 2.3 ng/mg protein) at 1 month after gonadectomy. Testosterone implants prevented the rise of Harderian gland somatostatin in castrated males. Gonadectomized males had lower somatostatin content in the gland than did control males (1.0 +/- 0.2 ng/mg protein) at 2 months after castration. Somatostatin values in females were unaffected by gonadectomy, but there were variations during the oestrous cycle, with a nadir detected at dioestrus-1 and maximal values coincident with the day of the ovulation.

Androgens↗
PubMed1987

Day-night rhythm of rat pineal tyrosine hydroxylase activity as determined by HPLC with amperometric detection.

Tyrosine hydroxylase activity in the rat pineal gland was measured by means of HPLC determination of the amount of L-3,4-dihydroxyphenylalanine formed. Enzyme activity showed a clear day-night rhythm, paralleling that of plasma melatonin levels in the same animals, with values being high during the dark period apparently because of changes in Vmax. In animals maintained under constant illumination for 3 days, tyrosine hydroxylase activity and plasma melatonin level rhythms were completely abolished, a result indicating that both are under photoperiodic control.

Animals↗