Effects of combined long-term treatment with a growth hormone-releasing hormone analogue and a growth hormone secretagogue in the growth hormone-releasing hormone knock out mouse

GH secretagogues (GHS) are synthetic ghrelin receptor agonists that stimulate GH secretion. It is not clear whether they act predominantly by stimulating the secretion of hypothalamic growth hormone-releasing hormone (GHRH), or directly on the somatotrope cells. In addition, it is not known whether combined treatment with GHRH and GHS has synergistic effects on growth. To address these questions, we used the GH-deficient GHRH knock out (GHRHKO) mouse model, which has severe somatotrope cell hypoplasia. We treated GHRHKO mice for 5 weeks (from week 1 to week 6 of age) with the GHRH analogue JI-38 alone, or in combination with a GHS (GHRP-2), and at the end of the treatment we examined their response to an acute stimulus with GHRP-2 or GHRP-2 plus JI-38. We used placebo-treated GHRHKO mice and animals heterozygous for the GHRHKO allele as controls. Animals treated with JI-38+GHRP-2 reached higher body length and weight than animals treated with JI-38 alone. All the animals receiving JI-38 (with or without GHRP-2) showed similar correction of somatotrope cell hypoplasia. None of the GHRHKO animals showed a serum GH response to the acute stimulation with GHRP-2 alone, while both treated groups responded to the combined test with JI-38 + GHRP-2. These data demonstrate that in GHRHKO mice, GHRP-2 has a growth-stimulating effect that augments the response induced by JI-38. In addition, the presence of GHRH seems necessary for the stimulation of GH secretion by GHRP-2.     

Response-specific and ligand dose-dependent modulation of estrogen receptor (ER) alpha activity by ERbeta in the uterus

Estrogen is of great importance in the regulation of uterine function. The aim of this study was to examine the individual physiological roles of each of the two receptors for estradiol, estrogen receptor (ER) alpha and ERbeta, and their potential comodulatory effects on gene expression and uterine growth using recently developed ER subtype-selective agonist ligands. The use of ER subtype-selective ligands provides an alternative, complementary approach to the use of receptor knockout mice. Administration of the ERalpha-selective ligand propyl pyrazole triol (PPT) to immature mice resulted in a significant increase in uterine weight, as well as bromodeoxyuridine incorporation and proliferating cell nuclear antigen expression in luminal epithelial cells. PPT also increased complement component 3, lactoferrin, and glucose-6-phosphate dehydrogenase (G6PDH), and decreased androgen receptor (AR) and progesterone receptor (PR) mRNA levels in uterine tissue, as did estradiol (E(2)). However, when compared with E(2), PPT was less effective in stimulating uterine weight, complement component 3, and G6PDH expression but was as effective as E(2) in regulating lactoferrin, AR, and PR expression. In contrast to the action of the ERalpha agonist PPT, the ERbeta agonist diarylpropionitrile (DPN) did not increase uterine weight or luminal epithelial cell proliferation at a dose that reduced G6PDH and elicited a decrease in PR and AR mRNA and protein expression. Interestingly, DPN reduced the uterine weight stimulation by PPT, and enhanced the effect of PPT in decreasing uterine PR and AR mRNA. These findings with ER subtype-selective ligands indicate that ERalpha is the major regulator of estrogen function in the uterus, but that ERbeta does exert effects on some uterine markers of estrogen action. In addition, ERbeta can modulate ERalpha activity in a response-specific and dose-dependent manner.     

Isolated follicle-stimulating hormone deficiency in man.

Two men with serum levels of follicle-stimulating hormone (FSH) persistently below 3 mIU/ml and normal levels of luteinizing hormone (LH), thyroid-stimulating hormone (TSH), growth hormone, prolactin, cortisol, and testosterone are reported. The intravenous administration of thyrotropin-releasing factor led to a normal increase in TSH and prolactin levels. Gonadotropin-releasing factor stimulation resulted in a net increase of 2 mIU/ml and 25 mIU/ml for FSH and LH, respectively. The administration of clomiphene resulted in a normal FSH increase in both patients, an LH increase in one, and a serum testosterone increase in the other. These results suggest a possible defect for FSH production at a level above the pituitary. Semen analyses revealed abnormalities in motility and morphology. A testicular biopsy from one patient revealed delayed maturation of spermatogenesis. It is recommended that serum FSH determinations be included in studies of male infertility patients.     

Pituitary gonadotropin response to LHRH in human pregnancy.

The effect of synthetic LHRH on serum levels of FSH, LH, and hCG was determined during early and midgestation. Eight healthy volunteers were studied during the first (8--9 weeks) and second (15--20 weeks) trimesters of pregnancy with 4 patients in each group. Serum samples, obtained before and 15, 30, 45, 90, 120, 150, and 180 minutes after an intravenous bolus of 100 microgram LHRH, were assayed for LH, FSH, and hCG by specific radioimmunoassays. Serum levels of estradiol, progesterone, and 17 alphahydroxyprogesterone were also measured in samples obtained prior to and 3 hours after LHRH injection. The serum levels of LH and FSH were undetectable in all samples, and no increase was observed after administration of LHRH. Levels of chorionic gonadadotropin, estradiol, progesterone, and 17alpha-hydroxyprogesterone did show slight fluctuations, but there was no significant effect from LHRH administration. These results support the concept that pituitary gonadotropic function is markedly suppressed during early human pregnancy.     

Cardiac Baroreflex during the Postoperative Period in Patients with Hypertension: Effect of Clonidine

Background: Patients with essential hypertension show altered baroreflex control of heart rate, and during the perioperative period they demonstrate increased circulatory instability. Clonidine has been shown to reduce perioperative circulatory instability. This study documents changes in measures of heart rate control after surgery in patients with essential hypertension and determines the effects of clonidine on postoperative heart rate control in these patients.

Methods: Using a randomized double-blind placebo-controlled design, 20 patients with essential hypertension (systolic pressure > 160 mmHg or diastolic pressure > 95 mmHg for >or= to 1 yr) were assigned to receive clonidine (or placebo), 6 [micro sign]g/kg orally 120 min before anesthesia and 3 [micro sign]g/kg intravenously over 60 min before the end of surgery. The spontaneous baroreflex ("sequence") technique and analysis of heart rate variability were used to quantify control of heart rate at baseline, before induction of anesthesia, and 1 and 3 h postoperatively.

Results: Baroreflex slope and heart rate variability were reduced postoperatively in patients given placebo but not those given clonidine. Clonidine resulted in greater postoperative baroreflex slope and power at all frequency ranges compared with placebo (4.9 +/- 2.9 vs. 2.2 +/- 2.1 ms/mmHg for baroreflex slope, 354 +/- 685 vs. 30 +/- 37 ms2/Hz for high frequency variability). Clonidine also resulted in lower concentrations of catecholamine, decreased mean heart rate and blood pressure, and decreased perioperative tachycardia and hypertension.     

The human ARHI tumor suppressor gene inhibits lactation and growth in transgenic mice

ARHI is a novel imprinted tumor suppressor gene. To study its function in vivo, we have developed transgenic mice that overexpress ARHI. Offspring bearing the transgene had significantly lower body weights than did nontransgenic littermates. In addition, strong expression of the ARHI transgene was associated with greatly impaired mammary gland development and lactation, failure of ovarian folliculogenesis resulting in decreased fertility, loss of neurons in the cerebellar cortex, and impaired development of the thymus. Decrease in body size and defects in the mammary glands correlated with the level of transgene expression. Immunohistochemical analysis indicated that expression of prolactin (PRL), but not growth hormone, was lower in the pituitary glands of mice with defective mammary gland development. The defect in pregnancy-associated mammary tissue proliferation was associated with decreased serum PRL and progesterone levels. Moreover, lower levels of estrogen receptor and progesterone receptor were observed in postpartum mammary glands and in the ovaries of mice that overexpressed ARHI. Our data suggest that ARHI can inhibit PRL secretion and act as a negative regulator in murine growth and development.