A rapid and simple method for labeling short DNA fragments using Taq polymerase

This report describes a new method for labeling PCR-generated short length (60-120 bp) double-stranded DNA fragments for use as hybridization probes. The method utilizes gene-specific primers identical to those for PCR generation of non-radioactive DNA fragments. Radioactive probes are synthesized by Taq DNA polymerase without using PCR. Single-stranded (sense or antisense) and double-stranded probes can be individually prepared by selection of the appropriate primers. The labeling reaction reached maximum incorporation within 30 min with mean specific activities of 1.05 x 10(9) dpm/microgram (antisense single-stranded), and 1.62 x 10(9) dpm/microgram (double-stranded) were obtained using templates 69-117 of nucleotides. This method offers a simple and rapid means of generating antisense probes for Northern blot analyses and double-stranded probes for Southern blot analyses that provide highly intense signals with low background.

Impaired generation of cyclic adenosine 3',5'-monophosphate in a somatomammotroph cell line derived from dwarf (dw) rat anterior pituitaries

The dwarf (dw) mutation in rats results in 40-50% growth retardation associated with a selective reduction in pituitary somatotroph number, GH content, and GH mRNA levels and a decreased GH secretory response to GH-releasing factor (GRF). Recent studies in freshly dispersed pituitary cells have provided evidence for a defect in adenylate cyclase-linked GRF signal transduction in dw somatotrophs. To further examine this defect in a more specific cell population, we developed a somatomammotroph cell line (DP) derived from anterior pituitaries of male dw rats. A similar cell line from normal rats (Po) was used as control. We studied acute GH (4-h release) and cAMP (30-min intracellular accumulation) responses to GH secretagogues known to interact with the adenylate cyclase system. Basal GH release in both cell lines was 80-130% of the cell content, thus limiting the capacity for further GH responses. GRF (10(-8) M) produced a doubling of cAMP levels in Po and DP cells (P less than 0.01), but inconsistent effects on GH release. (Bu)2cAMP (5 x 10(-3) M) increased GH secretion by 50-100% in both groups (P less than 0.01). Cholera toxin (10(-9) M) increased GH release by 50% in both Po and DP (P less than 0.01), but the cAMP response in DP cells was only half that in Po cells (P less than 0.01). Forskolin (10(-5) M), a direct stimulator of adenylate cyclase, doubled GH release in both groups (P less than 0.01). However, cAMP generation was impaired in DP, with a maximal response to forskolin less than one third that in Po (P less than 0.01). In somatotrophs, cAMP mediates not only GRF-stimulated GH release, but also GH synthesis and mitogenesis. The impairment in maximal cAMP generation in DP cells, while not affecting acute GH release, may underlie the defect in somatotroph cell number and GH content in the dw pituitary gland.

Biosynthesis of human growth hormone-releasing hormone (hGRH) in the pituitary of hGRH transgenic mice

We have studied the posttranslational processing of prohuman GH-releasing hormone (pro-hGRH) to the mature hormones, hGRH(1-44)-NH2 and hGRH(1-40)-OH, and its carboxyl-terminal peptide (hGCTP) in pituitary cells from transgenic mice bearing a metallothionein-hGRH fusion gene after incubation with [35S]methionine. After separation on HPLC, 35S-labeled and unlabeled hGRH in medium and cell extracts were characterized by RIA and immunoprecipitation with antisera against hGRH and against hGCTP. After a 4-h pulse, unlabeled and [35S]pro-hGRH, hGRH(1-44)-NH2, and hGRH(1-40)-OH were identified in medium and cell extracts by both RIA and immunoprecipitation with anti-hGRH serum. In cell extracts, after a 0.5-h pulse, [35S]pro-hGRH and hGRH(1-44)-NH2 but not [35S]hGRH(1-40)-OH were detectable. After a 0.5-h chase, however, 35S-labeled hGRH(1-40)-OH, pro-hGRH, and [35S]hGRH(1-44)-NH2 were all measurable. After a 4-h chase, comparable levels of [35S]hGRH(1-44)-NH2 and hGRH(1-40)-OH were present, and very little intracellular 35S-pro-hGRH remained. A progressive decrease in the ratio of immunoprecipitable pro-hGRH to mature hGRH peptides and an increase in the ratio of hGRH(1-40)-OH to hGRH(1-44)-NH2 was observed in the two chase periods. In medium, [35S]hGRH(1-44)-NH2 was detectable at all times, whereas only minimal amounts of [35S]hGRH(1-40)-OH were present. Labeled and unlabeled pro-hGRH in cell extracts was also detected with anti-hGCTP serum, and another peak, which coeluted with synthetic hGCTP, was also identified. The low molar ratio of intracellular immunoreactive hGCTP to hGRH (less than 0.02) suggests a more rapid turnover rate of hGCTP than of hGRH. These results demonstrate the processing of hGRH prohormone to both mature forms of hGRH and provide evidence that hGRH(1-40)-OH is derived from hGRH(1-44)-NH2.

Growth hormone and insulin-like growth factor-I measurements in high growth (hg) mice

Effects of a recessive gene causing high growth (hg) were studied on two major components of the growth axis in mice. Plasma and pituitary levels of growth hormone and plasma levels of insulin-like growth factor I (IGF-I) were measured in three lines homozygous for hg, each compared with a control line of alike genetic background but wild type for the hg locus (Hg). Line Gh (hghg) and line GH (HgHg) are from a line which had undergone long-term selection for high postweaning weight gain; line Ch (hghg) and line CH (HgHg) were extracted from the second backcross of Gh to C57BL/6J; line L54 (hghg) was from the sixth backcross to C57BL/6J (B6) (HgHg). Pituitary GH levels and plasma IGF-I levels were measured in both sexes at 3, 4.5, 6 and 9 wk of age. Plasma growth hormone was measured in 8- to 12-wk-old males at hourly intervals from 08.00 to 17.00. Body weight in lines homozygous for hg at 6 and 9 wk of age was 10-30% greater than in control lines. The ontogeny of this increased growth depended on genetic background. Pituitary growth hormone content was 52% lower in the two hghg lines measured (lines Ch and Gh) than in control lines at 4.5, 6 and 9 wk. Plasma growth hormone levels were also much lower in hg mice, with values only 20-30% of those in their respective controls. hg lines showed consistently low plasma growth hormone levels throughout the 9 hr sampling period, while control lines expressed the characteristic pulsatile hormone secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a defect in growth hormone-releasing factor signal transduction in the dwarf (dw/dw) rat pituitary

Dwarf (dw/dw) rats exhibit a 40% reduction in body growth, isolated GH deficiency (less than 5% of normal pituitary content), and a decreased number of pituitary somatotrophs (15-20% of normal). Since GH-releasing factor (GRF) stimulates GH synthesis and secretion and somatotroph proliferation, and its effects are probably mediated by cAMP, we have assessed GH secretion and cAMP production in dw rat pituitaries in response to various GH secretagogues. Dispersed pituitary cells from dw rats were less sensitive (2.5-fold) to stimulation of GH secretion by GRF and showed a 25% reduction in the maximal GH response even after normalization of their reduced GH content. Intracellular cAMP was elevated 63-fold over basal levels in normal cells after 4 h in response to maximal GRF stimulation, but only 1.9-fold in dw cells, and even larger differences between the groups were found at earlier time points. The GH responses of dw cells to exogenous cAMP, however, were indistinguishable from normal. Forskolin, a direct stimulator of adenylate cyclase, elicited comparable maximal GH and cAMP responses, but an increased ED50, in dw cells. Activation of GS alpha by cholera toxin showed an increased ED50 and reduced GH and cAMP responses in dw cells, and marked decreases in these responses were observed in response to prostaglandin E1. Phorbol ester stimulation resulted in a reduced maximal GH response in dw cells without a change in sensitivity. These results provide evidence for a defect in the GRF signal transduction pathway associated with a decreased ability of GS alpha to stimulate adenylate cyclase in dw rat somatotrophs that may be causally linked to their GH deficiency.

Synthesis and biological evaluation of mouse growth hormone-releasing factor

The recently described mouse growth hormone-releasing factor (mGRF) was synthesized by the solid phase procedure, purified by 2 stages of preparative high performance liquid chromatography and fully characterized. The biologic activity of the 42-amino acid peptide (H-His-Val-Asp-Ala-Ile-Phe- Thr-Thr-Asn-Tyr- Arg-Lys-Leu-Leu-Ser-Gln-Leu-Tyr-Ala-Arg-Lys-Val-Ile-Gln-Asp-Ile-Met-Asn- Lys- Gln-Gly-Glu-Arg-Ile- Gln-Glu-Gln-Arg-Ala-Arg-Leu-Ser-OH) was assessed in primary cultures of both mouse and rat anterior pituitary cells and compared to synthetic rat (rGRF) and human (hGRF) growth hormone-releasing factors. mGRF was equipotent to rGRF in mouse somatotrophs but slightly less potent in rat somatotrophs, while hGRF was 3-5 times less potent in both rodent species.

The role of the cholinergic pathway in growth hormone feedback

Cholinergic pathways play an important role in the regulation of GH secretion. To assess their participation in GH feedback, we investigated the effect of pyridostigmine (an acetylcholinesterase inhibitor) on plasma GH responses to GH-releasing hormone (GHRH) plus TRH, insulin hypoglycemia, and arginine as well as on the inhibition of these responses by exogenous GH. The GH response to each stimulus was inhibited by an infusion of GH (0.55 micrograms/m2/min), started 4 h earlier. Pyridostigmine (120 mg, orally), administered 30 min before the stimulus, enhanced GH responses to GHRH and insulin during both saline and GH infusions. However, GH responses during combined administration of pyridostigmine and GH were less than those during pyridostigmine alone. GH responses to arginine, in contrast, were not affected by pyridostigmine in either the absence or presence of exogenous GH. TSH responses to TRH were unaltered by either GH or pyridostigmine. Pyridostigmine enhancement of GH responses to a maximally stimulatory dose of GHRH suggests that its effect is exerted by inhibition of somatostatin release. The lack of effect of pyridostigmine on plasma GH responses to arginine suggests that arginine and pyridostigmine increase GH secretion through a common pathway. The enhancement by pyridostigmine of GH responses in both the presence and absence of exogenous GH suggests that exogenous GH and pyridostigmine exert their discordant effects on GH secretion through independent mechanisms.

Tissue-specific transcription initiation and effects of growth hormone (GH) deficiency on the regulation of mouse and rat GH-releasing hormone gene in hypothalamus and placenta

Hypothalamic GRH gene expression has been shown to be negatively regulated by GH in both rat and mouse. The recent reports of different 5' untranslated sequences in mouse GRH cDNA from hypothalamus and placenta have raised the possibility of tissue-specific regulation of the GRH gene. To provide support for this possibility, we have studied rodent models with GH deficiency due to genetic defects in the pituitary. Complementary DNA probes for the hypothalamic and placental 5' regions were used to determine the tissue specificity of each mRNA. Although the hypothalamic form of GRH mRNA was detected in placenta, it constituted less than 0.7% of total placental GRH mRNA. A placental 5' probe (based on the previously reported sequence) hybridized only with a larger mRNA species and was not tissue specific, indicating that it was not related to GRH and was derived possibly from a cloning artifact. The correct 5' sequence of mouse placental GRH cDNA was determined and shown to be distinct from both that previously reported and the hypothalamic sequence. Although the placental form of GRH mRNA was detected in hypothalamus using the polymerase chain reaction, its levels were undetectable by Northern blotting. The 5' end of rat placental GRH cDNA was similarly sequenced and shown to exhibit no homology with the rat 5' hypothalamic sequence, but a high degree of homology with the corresponding mouse placental sequence. In GH-deficient dwarf (dw/dw) rats, hypothalamic GRH mRNA levels were significantly increased above control levels in both females and males, and pregnancy did not alter the levels in either (dw) or control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of transcriptional regulatory element activities in transformed and non-transformed rat anterior pituitary cells

Transformed (GH-3) and non-transformed (P3) rat anterior pituitary cells were compared in their ability to direct expression of plasmids containing a variety of eukaryotic transcriptional regulatory elements (TREs). These include the herpes simplex virus thymidine kinase (HSV-TK), Rous sarcoma virus long terminal repeat (RSV-LTR), simian virus 40 early (SV-40E), human cytomegalovirus immediate-early (CMV-IE) and mouse metallothionein 1 (mMT-1) TREs. Chloramphenicol acetyl transferase (CAT) gene expression served as a reporter in this study. Following transient transfection, the cell lines exhibited similar profiles of TRE utilization. In each cell line. CMV-IE was most efficient in directing reporter gene expression, although 2-fold greater activity was observed in GH-3 versus P3 cells. RSV-LTR directed gene expression was lower than that of CMV-IE while both HSV-TK and SV-40E were inactive in each cell line. Also, the mMT-1 promoter was inducible by addition of ZnCl2 to the culture media, though the level required for maximal activation differed between the two cell lines. Transfected GH-3 and P3 cells, therefore, displayed similar TRE utilization profiles yet significant differences were observed in the ability of these cell lines to respond to specific regulatory elements.

Tissue distribution and molecular heterogeneity of human growth hormone-releasing factor in the transgenic mouse

Transgenic mice expressing the human growth hormone-releasing factor (hGRF) gene linked to the metallothionein promoter exhibit high circulating levels of hGRF and GH and increased growth. We have described the distribution of GRF immunoreactivity (GRF-IR) in various tissues and characterized its molecular heterogeneity using gel filtration and high performance liquid chromatography (HPLC) and two separate RIAs that recognized mid-molecule and carboxyl-terminal epitopes of hGRF. The highest levels of GRF-IR were in the pituitary, followed by the pancreas. Intermediate levels were present in hypothalamus and liver, and lower levels in visceral organs, heart, and gonads. The pituitary and brain revealed evidence of the two mature hormone forms [hGRF(1-44)-NH2 and hGRF(1-40)-OH and in addition a more hydrophobic form that is believed to represent the hGRF precursor (proGRF) on the basis of its estimated molecular size (approximately 9,000) and selective recognition by the mid-molecule RIA. The profiles of GRF in pancreas and gut were similar except that only minimal amounts of hGRF(1-40)-OH were detected. In contrast, neither mature hormonal form was present in the liver and plasma contained primarily hGRF(3-44)-NH2, the major circulating metabolite of hGRF. The results provide evidence for variable processing of the hGRF precursor that is tissue specific and indicate that several extrahypothalamic tissues possess the necessary complement of enzymes to generate the mature hormonal forms.

Somatostatin secretion and action in the regulation of growth hormone secretion

The inhibition of growth hormone (GH) secretion by the hypothalamic peptide, somatostatin, is mediated by two critical factors: the concentration of the peptide in hypothalamic portal plasma and the number of somatostatin (SRIF) receptors on the somatotroph. The secretory patterns of SRIF and GH-releasing hormone (GRH) in portal blood of unanesthetized sheep is pulsatile and a close relationship of GRH pulses to those of GH secretion was documented, while those of SRIF appear to have more of a modulatory role on the responses to GRH. Peripheral infusion of SRIF at a rate to provide concentrations comparable to those in the portal system leads to a desensitization of SRIF effects on the somatotroph, likely mediated by down-regulation of SRIF receptors. These effects are believed to modulate the GH responses to GRH secretion in the generation of pulsatile GH secretion.

Growth hormone and prolactin secretion in cultured somatomammotroph cells

A somatomammotropic cell line (P0) derived from adult rat pituitaries has been maintained in culture for 2 yr. Secretion of GH and PRL by this cell line has been studied in response to hypophysiotropic peptides known to affect the release of both hormones as well as agents that affect second messenger systems in an attempt to characterize the stimulus-secretion mechanisms used by these cells. GH and PRL release during short term (4 h) incubations of P0 cells and primary cultures of dispersed rat pituitary cells was initially measured in response to GRF, TRH, vasoactive intestinal peptide (VIP), and SRIF. In P0 cells, the minimal effective dose of each of the hypophysiotropic peptides was comparable with respect to GH and PRL secretion. The effects of TRH and VIP were similar to those in freshly dispersed cells with respect to PRL release, whereas those of GRF and SRIF were less potent with respect to GH release. The stimulation of GH and PRL release in P0 cells by adenylate cyclase-related agents ((Bu)2 cAMP and forskolin) was comparable to that for GH secretion in mature somatotrophs but much greater than that of PRL release in mature lactotrophs. Stimulation of GH and PRL release in P0 cells by protein kinase C-related agents (diacylglycerol and phorbol ester) was also similar to that observed for GH release from mature pituitary cells, whereas minimal or undetectable effects were observed on PRL release from mature cells. The results indicate that the P0 somatomammotropic cell line possesses receptors, second messenger systems, and secretory characteristics of both somatotrophs and lactotrophs, although where differences exist, there is more resemblance to somatotrophs. They also demonstrate that the responses to each of the agents studied are bihormonal and appear to be regulated by a common mechanism.

Impaired inhibitory effects of somatostatin on growth hormone (GH)-releasing hormone stimulation of GH secretion after short term infusion

We examined the effect of prior exposure to somatostatin (SRIH) on its inhibition of GH and TSH responses to GHRH and TRH stimulation to determine whether SRIH desensitization has physiological significance in man. Six men received GHRH (1 microgram/kg, iv) and TRH (0.3 microgram/kg, iv) 20 min after starting a saline or SRIH (5.5 ng/kg/min, iv) infusion and again 6 h later. Hormone responses were quantified by measuring the area under the curve, corrected for GH concentration at injection time. Similar results were obtained when GH responses were quantified by measuring the hormone secretory rate using the program Detect. Plasma GH and TSH responses to the two GHRH and TRH injections during saline were similar. However, the effects of prior exposure to SRIH were hormone specific. SRIH blunted GH responses to GHRH at 20 min (1609 +/- 286 micrograms/L.min vs. 451 +/- 224), but did not significantly inhibit the responses 6 h later (1422 +/- 410 micrograms/L.min vs. 1000 +/- 302). In contrast, SRIH inhibition of TSH responses to the two TRH injections was similar (first, 946 +/- 201 micrograms/L.min vs. 700 +/- 148; second, 813 +/- 175 micrograms/L.min vs. 562 +/- 66). We next used these results to study whether the previously reported attenuation of GH responses to repeated GHRH stimulation at 2-h intervals is mediated by SRIH. Eight men received GHRH (1 microgram/kg, iv) 380 min after starting a saline or SRIH (5.5 ng/kg/min, iv) infusion or 90 min after starting a primed (5 mg, iv) infusion of propranolol (80 micrograms/min, iv) and again 2 h later. As in the first protocol, GH responses to GHRH were not inhibited when preceded by a 6-h SRIH infusion. However, the 6-h SRIH infusion resulted in a partial restoration of plasma GH responses to the second GHRH injection (saline infusion: first, 1429 +/- 342 micrograms/L.min; second, 254 +/- 75; SRIH infusion: first, 1042 +/- 247 micrograms/L.min; second, 468 +/- 105). beta-Blockade by propranolol resulted in enhanced GH responses to GHRH, but did not prevent the attenuation of GH responses to the second GHRH injection (first, 1937 +/- 366 micrograms/L.min; second, 614 +/- 99). The desensitization to SRIH inhibition of GH responses to GHRH after a 6-h SRIH infusion provides evidence of physiological consequences of SRIH receptor down-regulation. The impaired GH responses to repeated GHRH stimulation are mediated at least in part by enhanced SRIH secretion, which appears independent of a beta-adrenergic mechanism.

Alterations in circulating human chorionic gonadotropin free alpha-subunit in insulin-dependent diabetic pregnancy: correlation with maternal characteristics

Circulating concentrations of hCG free alpha-subunit (alpha hCG) increase throughout pregnancy. To address the hypothesis that maternal plasma alpha hCG may reflect placental dysfunction and/or adverse perinatal outcome during insulin-dependent diabetic pregnancy, alpha hCG was measured serially throughout gestation, beginning before week 12, with a specific RIA using a monoclonal antibody in 54 insulin-dependent diabetic (randomly assigned to strict and customary glycemic control) and 25 nondiabetic pregnancies. alpha hCG was significantly lower in pregnant insulin-dependent diabetic subjects than in nondiabetics subjects until 24 weeks gestation, after which it was higher until delivery. Plasma alpha hCG stabilized in nondiabetics at 32 weeks, whereas it continued to increase in diabetics until delivery, at which time it was 37% greater than that in nondiabetics (mean +/- SE, 1441 +/- 90 vs. 1052 +/- 78 micrograms/L; P less than 0.002). Values in diabetic subjects assigned to strict control were intermediate between those in diabetic subjects assigned to customary control and nondiabetic subjects. alpha hCG was greater in diabetic subjects with pregestational hypertension or microvascular disease, but not in those with pregnancy-induced hypertension. These findings were independent of the assigned goals of glycemic control. alpha hCG was not correlated with the duration of diabetes or related to premature delivery, fetal distress, birth asphyxia, or macrosomia. Thus, alpha hCG is increased during the third trimester of the type I diabetic pregnancy and is associated with preexisting hypertension and maternal microangiopathy, but is not a predictor of adverse perinatal outcome. Excessive alpha hCG secretion in diabetes may share pathophysiological mechanisms in common with those underlying diabetic microangiopathy.

Measurement of growth hormone-releasing hormone and somatostatin in hypothalamic-portal plasma of unanesthetized sheep. Spontaneous secretion and response to insulin-induced hypoglycemia

To elucidate the role of growth hormone (GH)-releasing hormone (GRH) and somatostatin (SRIH) in the regulation of the growth hormone (GH) secretory pattern, we collected portal blood from five unanesthetized ovariectomized ewes for repeated measurements of GRH and SRIH simultaneous with those of peripheral GH. Hormones were measured at 10-min intervals for 5.5 h and their interrelationships analyzed. Mean portal GRH was 20.4 +/- 6.7 (SD) pg/ml and the estimated overall secretion rate was 13 pg/min. GRH secretion was pulsatile with peaks of 25-40 pg/ml and a mean pulse interval of 71 min. Mean portal SRIH was 72 +/- 33 pg/ml and the estimated overall secretion rate was 32 pg/min. SRIH secretion was also pulsatile with peaks of 65-160 pg/ml and a mean pulse interval of 54 min. The GH pulse interval was 62 min. A significant association was present between GRH and GH secretory peaks though not between GRH and SRIH or SRIH and GH. Insulin hypoglycemia resulted in a rapid and brief stimulation of SRIH secretion followed by a decline in GH levels. No effect was observed on GRH secretion until 90 min, when a slight increase occurred. The results suggest (a) the presence of an independent neural rhythmicity of GRH and SRIH secretion with a primary role of GRH in determining pulsatile GRH secretion, and (b) that the inhibitory effects of insulin hypoglycemia on GH in this species are attributable to a combination of enhanced SRIH secretion and possibly other factors, though without significant inhibition of GRH.

Expression of a cytomegalovirus-human growth hormone-releasing hormone precursor fusion gene in transfected GH3 cells

Pituitary GH3 cells were transfected with a human growth hormone-releasing hormone (hGRH) precursor minigene fused to the promoter region of either a cytomegalic immediate early gene (pCMV) or the mouse metallothionein-1 gene (mMT) to examine the molecular heterogeneity of the translation products. Expression of the hGRH message occurred following transfection of the cells with each fusion gene. Extracts of pCMV-hGRH-transfected GH3 cells as well as the culture medium contained detectable levels of immunoreactive (ir)-hGRH peptides. Analysis of molecular heterogeneity by reverse-phase high performance liquid chromatography and radioimmunoassay indicated that both mature forms of hGRH (hGRH(1-44)-NH2 and hGRH(1-40)-OH) were synthesized in the cells, although hGRH(1-44)-NH2 was the primary form secreted into the medium. A high molecular weight form of ir-hGRH, believed to represent the hGRH precursor (or a partially processed form of the precursor) was detected in cells and, in smaller amounts, in the medium. Several ir-hGRH peptides, presumed cleavage products of the mature forms of hGRH, were also found. The efficiency of processing of the hGRH precursor and metabolism of the mature hormonal forms in transfected cells grown in the presence of four different peptidase inhibitors varied with the inhibitor present. Transfected GH3 cells, therefore, possess all of the necessary enzymes for and are capable of processing the hGRH precursor to mature GRH and provide a model to study hGRH biosynthesis.

Lack of effect of drinking water barium on cardiovascular risk factors

Higher cardiovascular mortality has been associated in a single epidemiological study with higher levels of barium in drinking water. The purpose of this study was to determine whether drinking water barium at levels found in some U.S. communities alters the known risk factors for cardiovascular disease. Eleven healthy men completed a 10-week dose-response protocol in which diet was controlled (600 mg cholesterol; 40% fat, 40% carbohydrate, 20% protein; sodium and potassium controlled at the subject's pre-protocol estimated intake). Other aspects of the subjects' lifestyles known to affect cardiac risk factors were controlled, and the barium content (as barium chloride) of the drinking water (1.5 L/day) was varied from 0 (first 2 weeks), to 5 ppm (next 4 weeks), to 10 ppm (last 4 weeks). Multiple blood and urine samples, morning and evening blood pressure measurements, and 48-hr electrocardiographic monitoring were performed at each dose of barium. There were no changes in morning or evening systolic or diastolic blood pressures, plasma cholesterol or lipoprotein or apolipoprotein levels, serum potassium or glucose levels, or urine catecholamine levels. There were no arrhythmias related to barium exposure detected on continuous electrocardiographic monitoring. A trend was seen toward increased total serum calcium levels with exposure to barium, which was of borderline statistical significance and of doubtful clinical significance. In summary, drinking water barium at levels of 5 and 10 ppm did not appear to affect any of the known modifiable cardiovascular risk factors.

Effects of thyroid hormone deficiency and replacement on rat hypothalamic growth hormone (GH)-releasing hormone gene expression in vivo are mediated by GH

The role of thyroid hormone and GH in the regulation of hypothalamic GH-releasing hormone (GRH) gene expression in the rat was examined after the induction of thyroid hormone deficiency by thyroidectomy. Thyroidectomy resulted in a time-dependent decrease in hypothalamic GRH content, which was significant by 2 weeks postoperatively, and a reduction in pituitary GH content to 1% of the control level by 4 weeks. In contrast, GRH secretion by incubated hypothalami under both basal and K(+)-stimulated conditions was increased after thyroidectomy. Hypothalamic GRH mRNA levels also exhibited a time-dependent increase, which was significant at 1 week and maximal by 2 weeks after thyroidectomy. Administration of antirat GH serum to thyroidectomized rats resulted in a further increase in GRH mRNA levels. T4 treatment of thyroidectomized rats for 5 days, which also partially restored pituitary GH content, lowered the elevated GRH mRNA levels. However, comparable effects on GRH mRNA levels were observed by rat GH treatment alone. These results suggest that the changes in hypothalamic GRH gene expression after thyroidectomy in the rat are due to the GH deficiency caused by thyroidectomy, rather than a direct effect of thyroid hormone on the hypothalamus, since the changes were reversible by GH alone despite persistent thyroid hormone deficiency. In addition, they further support the role of GH as a physiological negative feedback regulator of GRH gene expression.

Beta-adrenergic modulation of growth hormone (GH) autofeedback on sleep-associated and pharmacologically induced GH secretion

To determine whether GH feedback affects both induced and spontaneous GH secretion and to explore its neurotransmitter mediation, we assessed the effects of 6-h GH infusions (0.55-5.5 micrograms/m2/min) on sleep-associated and GH-releasing hormone (GHRH)-, insulin hypoglycemia-, and arginine-stimulated GH secretion and their modulation by beta-adrenergic blockade in normal men. GH infusions initiated 2 h before the expected onset of sleep produced a dose-dependent inhibition of GH secretion. GH infusions (0.55 micrograms/m2/min) initiated 4 h before the stimuli inhibited the GH response to each, but did not alter the TSH response to TRH. Propranolol infusion (80 micrograms/min) started 2 h before the onset of sleep or the stimulus enhanced GH responses to GHRH and insulin alone and in the presence of GH. In contrast, propranolol neither enhanced the GH responses to arginine or sleep nor reversed the inhibitory effects of GH. The negative feedback effect of GH to both physiological and pharmacological stimuli of GH secretion indicates that it is most likely mediated by both stimulation of somatostatin and inhibition of GHRH release. The effects of beta-adrenergic blockade suggest an inhibition of somatostatin release, although the complex interaction of GH and propranolol implies that they act through dissimilar mechanisms.

Cloning and characterization of mouse growth hormone-releasing hormone (GRH) complementary DNA: increased GRH messenger RNA levels in the growth hormone-deficient lit/lit mouse

We have isolated and cloned the full length cDNA for mouse GH-releasing hormone (mGRH) from mouse hypothalamus using a recently described strategy involving the polymerase chain reaction technique (PCR). Degenerate oligonucleotide primers were selected based on short (six amino acids) conserved regions in the human and rat GRH peptides that would recognize DNA sequences encoding similar amino acids regardless of codon usage. Primer-extended cDNA was amplified by PCR on cDNA templates prepared by reverse transcribing total mouse hypothalamic RNA. After cloning and sequencing the initial product, the 3' and 5' ends of mGRH were generated using a separate PCR strategy (RACE protocol). The mGRH cDNA encodes a 103-amino acid reading frame, structurally similar to the human and rat GRH genes, containing a signal sequence, a 42-residue GRH peptide, and a 31-residue C-terminal region. Although the structures of mouse and rat GRH are highly conserved in the signal peptide and C-terminal region, there is considerable diversity in the GRH region, which exhibits nearly comparable homology with the rat (68%) and human (62%) structures. Differences between mouse and rat GRH were also found in the amino acid cleavage sites at the 5' and 3' ends of the mature peptide and at the polyadenylation signal.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of radio-frequency and electrolytic lesions of the paraventricular hypothalamic nucleus

Radio-frequency and anodal electrolytic lesions of the paraventricular nucleus (PVN) were found to produce equal and dramatic increases in body weight in female rats. Neither of the groups with lesions had significantly elevated plasma insulin levels during a period of food restriction, but individual values varied greatly. Both groups displayed marked basal hyperinsulinemia after 30 days of food ad lib. It is concluded that radio-frequency and electrolytic PVN lesions produce similar obesity syndromes.

Immunohistochemical analysis of human growth hormone-releasing hormone gene expression in transgenic mice

The tissue-specific expression of a fusion gene encoding the mouse metallothionein-1 promoter and the coding region of the human GH-releasing hormone (hGRH) gene was studied in transgenic mice by immunohistochemistry using an anti-hGRH serum that does not recognize endogenous mouse GRH. hGRH immunoreactivity (GRH-IR) was detected in specific cells of the pituitary, pancreas, kidney, duodenum, lung, testis, ovary, adrenal, heart, and brain. In the pituitary, using double immunofluorescent staining, GRH-IR was found in some, but not all, somatotrophs, gonadotrophs, thyrotrophs, and mammotrophs. GRH-IR was found in both pancreatic exocrine cells and endocrine islets. Within the islet, GRH-IR was colocalized in A and D cells with glucagon and somatostatin, respectively. Immunopositive cells in other tissues were localized in kidney proximal convoluted tubules, duodenal submucosal glands of Brunner, the smooth muscles of pulmonary arterioles, testicular Leydig cells, oocytes, adrenal medullary chromaffin cells, and cardiac atria. In the brain, GRH-IR was seen in the external layer of the median eminence and in perikarya and fibers of the hypothalamic arcuate nucleus, the parvocellular region of the paraventricular nucleus, the supraoptic nucleus, and the amygdala. Somatostatin-immunoreactive cell bodies and fibers in transgenic and control mouse hypothalamus were not appreciably different. In summary, hGRH expression in transgenic mice occurs in a cell-specific manner in the hypothalamus as well as in numerous other tissues, many of which have secretory functions.