Circadian variation of adrenocortical cyclic nucleotides (cyclic AMP and cyclic GMP) in hypophysectomized rats

Summary The existence of a circadian variation in the adrenocortical concentrations of cyclic AMP and cyclic GMP in male adult Wistar rats examined 10 days after hypophysectomy is demonstrated. The results suggest that the circadian variations of adrenocortical cyclic nucleotides observed previously in intact rats might not entirely depend upon pituitary corticotrophin.Acknowledgment. Thanks are due to Prof. J. M. Racadot and Dr Y. Drouet for their assistance with the histological examinations.     

Altered brain cyclic AMP-responses in rats reared in enriched or impoverished environments

Summary The accumulation of radioactive cyclic AMP elicited by various neurohormones has been examined in adenine-labeled telencephalon slices from rats raised in enriched or impoverished environments. Basal levels of cyclic AMP and responses of the brain slice cyclic AMP-generating systems to norepinephrine, isoproterenol and adenosine did not differe between the two group of rats, while responses to prostaglandin E₁ were significantly greater with the impoverished group and responses to histamine appeared to be greater with the enriched group.     

Altered brain cyclic AMP-responses in rats reared in enriched or impoverished environments.

The accumulation of radioactive cyclic AMP elicited by various neurohormones has been examined in adenine-labeled telencephalon slices from rats raised in enriched or impoverished environments. Basal levels of cyclic AMP and responses of the brain slice cyclic AMP-generating systems to norepinephrine, isoproterenol and adenosine did not differ between the two group of rats, while responses to prostaglandin E1 were significantly greater with the impoverished group and responses to histamine appeared to be greater with the enriched group.     

Timing of single daily meal influences relations among human circadian rhythms in urinary cyclic AMP and hemic glucagon, insulin and iron.

Relations among circadian rhythms in serum iron, glucagon and insulin and urinary cyclic AMP excretion differ drastically when diurnally active, nocturnally resting human adults consume all daily food for one week as breakfast only and for another week as dinner only - a finding of interest to diverse fields, e.g., for optimizing certain kinds of therapy or for a better utilization of calories.     

Monolayer cultures of normal adult rat adrenocortical cells: steroidogenic responses to nucleotides, bacterial toxins and antimicrotubular agents.

Monolayer cultures of normal rat adrenocortical cells were treated with agents which stimulate steroidogenesis by Y-1 adrenal tumour cells. Choleragen was active, whereas cyclic nucleotides other than cyclic AMP, bacterial endotoxins and antimicrotubular agents were inactive.     

Timing of single daily meal influences relations among human circadian rhythms in urinary cyclic AMP and hemic glucagon,insulin and iron

Summary Relations among circadian rhythms in serum iron, glucagon and insulin and urinary cyclic AMP excretion differ drastically when diurnally active, nocturnally resting human adults consume all daily food for one week as breakfast only and for another week as dinner only—a finding of interest to diverse fields, e.g., for optimizing certain kinds of therapy or for a better utilization of calories.Supported by grants (No. RR-400 from the General Clinical Research Centers Program of the Division of Research Resources, National Institutes of Health, USPHS and Nos. 5-K6-GM-13, 981 and 1RO1-CA-14445-01) and grant No. 20, Fondation de l'industrie pharmaceutique pour la recherche.     

Pineal-related changes in cyclic AMP levels of rat medial basal hypothalamus

Summary Pinealectomy (Px) in adult male rats resulted in increased cyclic AMP accumulation by medial basal hypothalamic (MBH) explants 3 and 7 days after surgery. 24 h after superior cervical ganglionectomy (Gx) an augmented MBH cyclic AMP accumulation was observed. The effects of Px and Gx were additive, as revealed in animals subjected to Gx 3 days after Px.This study was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (N^o 6638) and from the Fundación Alberto J. Roemmers, Argentina.     

Functional absence of brain photoreceptors mediating entrainment of circadian rhythms in the adult rat

Summary The photic energy penetrating into the brain was increased in adult rats sustaining craniotomies sealed with transparent plastic. After blinding, these animals failed to entrain their circadian food intake rhythm to light-dark cycles. Short pulses of light did not phase-shift the freerunning rhythm. We conclude that adult rats lack brain photoreceptors mediating entrainment of circadian rhythms.     

Monolayer cultures of normal adult rat adrenocortical cells: Steroidogenic responses to nucleotides,bacterial toxins and antimicrotubular agents

Summary Monolayer cultures of normal rat adrenocortical cells were treated with agents which stimulate steroidogenesis by Y-1 adrenal tumour cells. Choleragen was active, whereas cyclic nucleotides other than cyclic AMP, bacterial endotoxins and antimicrotubular agents were inactive.This work was supported by the Medical Research Council of Great Britain (grant No. 970/656/B). I am grateful to MissR. Magee for technical assistance and Prof.A. M. Neville for continued support.     

Circadian rhythm of plasma corticosterone in vagotomized rats

Summary In vagotomized rats, 2 weeks after surgery, the amplitude of the circadian rhythm of plasma corticosterone was extremely low, indicating that gastrointestinal activity may be in part involved in the hypothalamo-hypophyseal circadian rhythmicity.     

Plasma cyclic 3',5'-guanosine monophosphate and cyclic 3',5'-adenosine monophosphate response to methacholine in man

Cholinergic agents are known to induce increases in tissue and plasma levels of cyclic GMP in experimental animals. We observed that i.m. injection of methacholine, a cholinergic agent, caused significant increases in plasma cyclic GMP and cyclic AMP in man.     

Plasma cyclic 3′,5′-guanosine monophosphate and cyclic 3′,5′-adenosine monophosphate response to methacholine in man

Summary Cholinergic agents are known to induce increases in tissue and plasma levels of cyclic GMP in experimental animals. We observed that i.m. injection of methacholine, a cholinergic agent, caused significant increases in plasma cyclic GMP and cyclic AMP in man.     

Variations of cyclic nucleotide monophosphate levels during spontaneous uterine contractions.

Oscillations on the concentrations of cyclic nucliotides occurred during spontaneous rhythmic contractions in rat uterus. The levels of cyclic GMP and cyclic AMP were highest at the beginning of the contraction respectively the relaxation.     

Increased urinary excretion of cyclic nucleotides in X-linked hypophosphatemic (Hyp) mice

Hyp mice, a model for human X-linked hypophosphatemia, had elevated urinary cyclic AMP, cyclic GMP, and magnesium excretion compared to normal mice. The data suggest a renal origin of the urinary cyclic nucleotides. No significant differences in plasma cyclic AMP and cyclic GMP were observed between genotypes.     

Increased urinary excretion of cyclic nucleotides in X-linked hypophosphatemic (Hyp) mice

Summary Hyp mice, a model for human X-linked hypophosphatemia, had elevated urinary cyclic AMP, cyclic GMP, and magnesium excretion compared to normal mice. The data suggest a renal origin of the urinary cyclic nucleotides. No significant differences in plasma cyclic AMP and cyclic GMP were observed between genotypes.This work was supported in part by research grants from The Kroc Foundation and the NIH, RR-09016.     

Evidence for a modulation of the stress response by the pineal gland

Wistar rats show a circadian variation in their response to stress. Pinealectomy exacerbates stress-induced gastric ulceration in rats. This effect is counteracted by melatonin administration.     

Evidence for a modulation of the stress response by the pineal gland

Summary Wistar rats show a circadian variation in their response to stress. Pinealectomy exacerbates stress-induced gastric ulceration in rats. This effect is counteracted by melatonin administration.     

Corticotropin releasing factor increases the adrenocortical responsiveness to adrenocorticotropin

Summary In the course of studying the plasma adrenocorticotropic hormone (ACTH) and corticosterone responses to synthetic corticotropin releasing factor (CRF), we noted some disparity in the responses. A higher dose (20 g compared with 5 g per rat i.a.) produced an equal plasma ACTH but greater plasma corticosterone response in adult male rats. Thus, we examined the possibility that CRF increases adrenocortical responsiveness to ACTH. CRF significantly (p<0.0005) increased the plasma corticosterone response to ACTH in rats pretreated with dexamethasone. Thus, synthetic CRF increases corticosterone secretion in rats not only by stimulating ACTH secretion, but also by increasing the adrenocortical responsiveness to ACTH.Acknowledgments. This research was supported by grant MT-5183 from the Medical Research Council of Canada and by the Department of Medicine, University of Kentucky.     

Allergic reactions, cyclic AMP and histamine release.

Both isobutylmethylxanthine and theophylline increased the level cyclic AMP in the mast cell. Theophylline reduced the allergic histamine release, whereas isobutylmethylxynthine caused a pronounced potentiation of the histamine release. This indicates that the hypothesis of an inverse relationship between the level of cyclic AMP in mast cells and histamine release is too simple.     

Ontogenetic changes in relative levels of cyclic AMP-dependent and cyclic GMP-dependent protein kinases in prostates, epididymides and testes from guinea-pigs.

Changes in relative levels of cyclic AMP-dependent protein kinase (A-PK) and cyclic GMP-dependent protein kinase (G-PK) in prostates, epidymides and testes from guinea-pigs were examined at 3 different ages. During postnatal development, a decrease in the ratio of the 2 classes of protein kinases was seen in prostates, whereas increases of the ratios of the enzymes were found in epididymides and testes.