Hormones episodic release

Many hormones are released into the blood in a spasmodic and irregular manner. In this case, their concentrations change in an episodic or pulsatile fashion. This applies, for instance, to luteinizing hormone (LH, lutropin). 

The episodic release of growth hormone is the most pronounced among the pituitary hormones. Serum levels between bursts of release are usually low (<5... 

The episodic secretion of the hypothalamic hormone, gonadotrophin-releasing hormone (GnRH), stimulates synthesis and release of the gonadotrophins. LH (luteinizing hormone) and FSH (follicle-stimulating hormone), from the anterior pituitary. Despite the names, both gontidotrophins act cooperatively on the ovaries in the woman and the testes in the man to stimulate sex hormone secretion and reproductive processes. 

Primary therapy is based on disease severity and type of hemorrhage.7 Most patients with mild to moderate disease and a minor bleeding episode can be treated with l-desamino-8-D-arginine vasopressin [desmopressin acetate (DDAVP)], a synthetic analog of the antidiuretic hormone vasopressin. DDAVP causes release of von Willebrand factor (vWF) and factor VIII from endogenous storage sites. This formulation increases plasma factor VIII levels by three- to fivefold within 30 minutes. The recommended dose is 0.3 mcg/kg intravenously (in 50 mL normal saline infused over 15 to 30 minutes) or subcutaneously or 300 meg intranasally via concentrated nasal spray every 12 hours. Peak effect with intranasal administration occurs 60 to 90 minutes after administration, which is somewhat later than with intravenous administration. Desmopressin infusion may be administered daily for up to 2 to 3 days. Tachyphylaxis, an attenuated response with repeated administration, may occur after several doses.8... 

Condon TP, Dykshoon-Bosch MA, Kelly MJ (1988) Episodic luteinizing-hormone release in the ovariectomized female guinea pig rapid inhibition by estrogen. Biol Reprod 38 121-126... 

Lithium blocks the release of thyroid hormones, which are known to potentiate b-noradrenergic receptor sensitivity. This has led to the speculation that excessive thyroid activity may contribute to an episode of mania in susceptible patients, and that the antimanic effect of lithium is, at least in part, due to its antithyroid action (26). In this context, CBZ can also decrease various thyroid indices. 

Lithium Plus Thyroid Supplementation. Treatment-resistant and rapid-cycling bipolar patients may have an increased frequency of thyroid dysfunction. Further, some patients suffer from subclinical hypothyroidism and improve with the addition of thyroid supplementation. In this context, several case reports involving this population found that high doses of the thyroid hormone levothyroxine sodium (T ) were clinically beneficial (122,123 and 124). Kusalic (1.25) found that 6 of 10 rapid cyclers had hypothyroidism, based on their thyrotropin-releasing hormone stimulation tests. Further, the average number of mood episodes per year decreased by more than 75% (i.e., from 9.7 to 2.2) after thyroxine was added to the treatment regimen. 

During the acute phase of a viral infection of the thyroid gland, there is destruction of thyroid parenchyma with transient release of stored thyroid hormones. A similar state may occur in patients with Hashimoto s thyroiditis. These episodes of transient thyrotoxicosis have been termed "spontaneously resolving hyperthyroidism." Supportive therapy is usually all that is necessary, such as propranolol for tachycardia and aspirin or nonsteroidal anti-inflammatory drugs to control local pain and fever. Corticosteroids may be necessary in severe cases to control the inflammation. 

The neurons that elaborate hypophysiotropic hormones are themselves influenced by hypothalamic neurotransmitters, such as dopamine, norepinephrine, serotonin, acetylcholine, and endorphins. These neurotransmitters also modify the secretory activity of anterior pituitary hormones (see Table 50- i). Indeed basal and episodic secretion, diurnal rhythm, and nocturnal release of pituitary hormones are all considered to be secondary to central nervous system events that are mediated through hypothalamic hormones. 

Biorhythms and other physiological events in the brain result in episodic and circadian secretion of CRH from the hypothalamus. Tliis in turn elicits similar circadian variation in ACTH release. Secreted ACTH then stimulates cortisol production, which provides negative feedback inhibition to the CRH-ACTH axis. The secretion of CRH, a 41-amino acid peptide, is modulated by neuroendocrine, physical, and emotional factors. Besides CRH, other circulating factors can have an influence on the secretory dynamics of ACTH release. Antidiuretic hormone from the... 

Modalities to prevent priapism are limited and not well studied. Pseudoephedrine (30 or 60 mg/day given orally at bedtime) and leuprolide, a gonadotropin-releasing hormone, have been used to decrease the number of recurrent episodes of priapism. Hydroxyurea therapy may also be useful. Recently, low-doses of an antiandrogen, bicalutamide, have been used in two patients with SCD and one patient with spinal cord injury for treatment of recurrent and refractory priapism without major side effects. " " ... 

Millard et ai, 1987 Johnson, 1988 Asplin et al., 1989 Winer, Shaw Baumann, 1990). Thus, in the rat (fig. 8.22), while the higher frequency in GH release in the female results in quasi-constant levels of the hormone, well-defined secretory episodes occur in the male, with a frequency of one pulse every 3-4 h the pulses are separated by intervals of 2-2.5 h during which GH drops down to barely detectable levels (Waxman et ai, 1991). The ultradian rhythmic secretion of GH appears to result from the antagonistic effects of pulsatile stimulation by GH-releasing factor (GHRH Gelato Merriam, 1986) and inhibition by somatostatin (Tanenbaum Ling, 1984 Martha et al, 1988). 

Rasmussen, D.D. 1993. Episodic gonadotropin-releasing hormone release from the rat isolated median eminence in vitro. Neuroendocrinology 58 511-18. 

Thus it would appear that the immediate effect of a single suckling episode, i.e. acute suckling, is to reduce the prolactin content of the anterior pituitary gland with a release of the hormone into the circulation. The overall importance of suckling to lactation has been adequately reviewed (20-24). 

---