Alpha-helical-corticotropin-releasing hormone reverses anxiogenic effects of C-type natriuretic peptide in rats.

Previously we have shown that atrial natriuretic peptide (ANP) has anxiolytic-like properties after intraperitoneal, intracerebroventricular and intraamygdala infusion in rats. Since C-type natriuretic peptide (CNP) exerts endocrine and behavioral effects opposing those of ANP, we characterized the behavioral properties of CNP after icv infusion in rats by their performance in the elevated plus maze with and without the corticotropin-releasing hormone (CRH) antagonist alpha-helical-CRH (alpha-CRH). Low CNP doses of 0.05 microg icv or 0.1 microg icv did not significantly influence the behavior of rats in the plus maze. At higher doses (0.5 microg, 2 microg, 5 microg icv) CNP had distinct anxiogenic properties. Our hypothesis that corticotropin-releasing hormone (CRH) is involved, which elicits anxiety-like behavior, was examined by icv coadministration of alpha-CRH, an antagonist at CRH-1 and CRH-2-receptors. Icv alpha-CRH alone had no intrinsic anxiolytic properties at a dose of 25 microg. The anxiogenic effects of 2 microg CNP icv seen in the plus maze were entirely blocked by alpha-CRH. Directly after exposition ACTH and corticosterone levels did not differ between the groups, but after 30 min ACTH levels were significantly higher in the CNP-treated group compared to alpha-CRH/CNP-treated animals. Corticosterone was found significantly lowered in the alpha-CRH/saline group compared to the CNP treated group but not compared to saline controls. Our data suggest opposing effects of CNP and ANP on anxiety-related behavior and neuroendocrine regulation in rats, which appear to be mediated via different receptor occupation and brain regions, and by a CRH-dependent mechanism.

Targeted disruption of the orphanin FQ/nociceptin gene increases stress susceptibility and impairs stress adaptation in mice.

The neuropeptide orphanin FQ (also known as nociceptin; OFQ/N) has been implicated in modulating stress-related behavior. OFQ/N was demonstrated to reverse stress-induced analgesia and possess anxiolytic-like activity after central administration. To further study physiological functions of OFQ/N, we have generated OFQ/N-deficient mice by targeted disruption of the OFQ/N gene. Homozygous mice display increased anxiety-like behavior when exposed to a novel and threatening environment. OFQ/N-null mice show elevated basal pain threshold but develop normal stress-induced analgesia. Interestingly, these mice show impaired adaptation to repeated stress when compared with wild-type mice, whereas their performance in spatial learning remained unaffected. Basal and poststress plasma corticosterone levels were found to be elevated in OFQ/N-deficient animals. Thus, OFQ/N appears to be crucially involved in the neurobiological regulation of stress-coping behavior and fear.

Sleep endocrine effects of megestrol acetate in healthy men.

Synthetic and naturally occurring steroids exert a variety of neural effects that include modulation of nocturnal sleep. The present study focuses on the effect of progesterone receptor (PR) activation on the nocturnal sleep electroencephalogram (EEG) in male volunteers. As a PR ligand, the synthetic progesterone megestrol was used, which has the advantage over progesterone in that it is not metabolized into other steroid compounds which could cloud the progesterone-mediated effects through their own neuroactive properties. Nine healthy male volunteers were investigated in a prospective single-blind randomized study design. They received either placebo tablets or megestrol acetate dosages of 160, 320 or 480 mg at 14.00 h and 19.00 h. Blood samples were drawn half-hourly from 22.00 h until 07.00 h. After 320 mg megestrol, plasma adrenocorticotropin secretion was lower and growth hormone secretion was higher than after 160 mg and 480 mg megestrol or placebo. Similarly, the reduction in the relative amount of rapid eye movement sleep was most pronounced after 320 mg. Thus, progesterone receptor activation, as reflected by the sleep EEG and associated pituitary hormone secretion, follows a nonlinear U-shape dose dependency of a well-defined PR ligand, which may explain the unresolved inconsistencies of neuroendocrine progesterone effects to date. Moreover, employing a CV1 cell line, contransfected with a human glucocorticoid receptor expression vector and a reporter gene-based detection system for transcriptional activity, revealed that a PR agonist such as megestrol may also activate glucocorticoid receptors. This may account for some of the neuroendocrine effects of megestrol and other progestins.

Atrial natriuretic hormone in lactate-induced panic attacks: mode of release and endocrine and pathophysiological consequences.

Previous studies have shown unequivocally a lack of pituitary-adrenocortical stress hormone activation during lactate-induced panic attacks despite considerable psychopathological alterations, signs of arousal and several vegetative symptoms regularly occurring during stressful conditions. To study the possible inhibitory action of atrial natriuretic hormone (ANH) on adrenocorticotrophic hormone (ACTH) and cortisol release in humans, 10 patients with panic disorder (DSM-III-R) received sodium lactate and placebo (0.9% saline) infusions and ten healthy comparison subjects additionally received a 2.5% saline infusion and the response of ANH, vasopressin, ACTH, cortisol, and several biochemical and physiological cardiovascular parameters were measured. In comparison to placebo, lactate infusion led to enhanced ANH levels in both non-panicking comparison subjects and panickers. Importantly, panickers showed significantly lower baseline levels of ANH than comparison subjects followed by a faster release. No significant concomitant changes in vasopressin, ACTH, and cortisol were observed. During lactate infusion, heart rate was accelerated considerably in the two groups; in contrast, the reduction of pCO2 indicated an enhanced ventilation only in panickers. The pattern of ANH release cannot be attributed simply to either the volume load administered, the cardiac activation or an osmotic effect since neither 0.9 nor 2.5% saline resulted in comparable effects. Additional central nervous mechanisms must be considered for the increased ANH concentrations in lactate-induced panic attacks. We propose that the release of ANH is an intrinsic mechanism contributing to the apparent unresponsiveness of the pituitary-adrenocortical system in lactate-induced panic attacks. In addition, we surmise that ANH may also play a role in the yet unknown mechanisms for termination of panic attacks, e.g. either by inhibitory actions on the locus coeruleus or by bronchiorelaxation and consecutive decatastrophization.

Sleep-endocrine effects of mifepristone and megestrol acetate in healthy men.

Administration of steroid hormones was demonstrated to modulate the sleep electroencephalogram (EEG) and sleep-associated hormonal secretion in specific ways. The present study was conducted to compare the effects of mifepristone (Mif), a mixed glucocorticoid (GR) and progesterone receptor (PR) antagonist, and megestrol acetate (Meg), a PR agonist. Nine healthy men were pretreated with either placebo or 200 mg Mif or 320 mg Meg, or a combination of both. Changes in plasma adrenocorticotropic hormone (ACTH), cortisol, and growth hormone concentrations were registered every 30 min; sleep EEG recordings were obtained continuously. Administration of Mif increased the morning plasma ACTH and cortisol surges, whereas Meg had the opposite effect. Growth hormone secretion was lowered by Mif pretreatment and enhanced by Meg. Simultaneous administration of both compounds led to largely compensated effects. The sleep EEG changes induced by Mif were a slight increase in the time awake and a delayed onset of slow-wave sleep. Meg led to a reduction of rapid-eye-movement sleep. Simultaneous administration of Mif and Meg showed a synergism in increasing time awake and shallow sleep: it therefore may be concluded that the sleep EEG effects are mediated by an interaction of GR and PR in unknown mechanisms.

C-type natriuretic peptide exerts stimulatory effects on the corticotropin-releasing hormone-induced secretion of hormones in normal man.

C-type natriuretic peptide and atrial natriuretic peptide have been reported to bind to distinct receptors and to exert opposing effects on different systems. Although it is known that atrial natriuretic peptide inhibits the corticotropin-releasing hormone-stimulated hormone release in man, the corresponding action of C-type natriuretic peptide has so far not been characterized. We investigated the effects of 30-min infusions of 150 and 300 micrograms C-type natriuretic peptide on adrenocorticotropin, cortisol, and prolactin release stimulated by 100 micrograms corticotropin-releasing hormone and on cardiovascular parameters in 8 healthy male volunteers. Compared with placebo, 300 micrograms C-type natriuretic peptide significantly (P < 0.05) enhanced the stimulation of cortisol (area under curve (arbitrary units): 520 +/- 35 vs 651 +/- 55) and prolactin (area under curve: 29 +/- 3 vs 37 +/- 5). Adrenocorticotropin levels were increased, but the differences did not reach statistical significance (maximum increment: 27 +/- 4 vs 36 +/- 2 pg/ml). C-type natriuretic peptide at a dose of 150 micrograms had no clear effect on these hormones and C-type natriuretic peptide also produced no cardiovascular or subjective effects. Our data suggest stimulatory effects of C-type natriuretic peptide on corticotropin-releasing hormone-induced hormone release and offer further evidence for a complex role of different natriuretic peptides in endocrine regulation.