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W J DeVito

Publications and source records attributed to W J DeVito.

At least 37 records · Page 2Linked to original sources
PubMed1992

Proteolytic modification of prolactin by the female rat brain.

Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analyses we have identified immunoreactive prolactin (PRL) proteins with molecular weights of 24 and 16 kD in the female rat brain. Because PRL target tissues have been shown to contain enzymes which, in vitro, cleave PRL into a 16-kD PRL fragment, studies were performed to characterize PRL proteolysis in the female rat brain. In vitro proteolysis of PRL was examined by incubating [125]I-PRL with 25,000 g subcellular fractions followed by SDS-PAGE under reducing conditions. At acidic pHs, incubation of PRL with 25,000 g hypothalamic fractions consistently resulted in the generation of a 16-kD fragment. The generation of the 16-kD fragment was time and tissue concentration dependent. Enzyme inhibitor analysis indicated that PRL proteolysis could be blocked by aspartate and serine protease inhibitors, but not sulfhydryl, metalloenzyme or trypsin protease inhibitors. Subcellular localization of hypothalamic PRL proteolytic activity by equilibrium density centrifugation revealed a bimodal distribution of proteolytic activity with modal densities of 1.12 and 1.24 g/ml. Homogenization of the tissue in a hypo-osmotic medium disrupted the high density peak resulting in a single low-density peak at the top of the gradient. These data indicate that subcellular fractions of the rat brain contain enzymes which can cleave PRL into a 16-kD fragment under acidic conditions. The majority of the enzymatic activity is localized in membrane-bound particles with a density similar to subcellular particles which contain PRL.

Animals↗
PubMed1992

Prolactin-stimulated mitogenesis of cultured astrocytes.

PRL has been reported to activate cell cycle-specific enzyme markers in nonreproductive tissues. To determine if PRL stimulates cell cycle-specific markers and cell growth in the central nervous system, the effect of PRL on cellular proliferation was examined in cultured astrocytes. Astrocytes from confluent cultures were plated onto glass slides at a density of 2 x 10(4) cell/ml 24 h before use. In some experiments, cells were serum deprived for 24 h (Go-arrested) after plating. Cell proliferation was examined directly by an increase in cell number and in individual cells by immunofluorescent detection of proliferating cell nuclear antigen (PCNA) and the incorporation of 5-bromo-2'-deoxyuridine (BrUd). When incubated with 1% serum, a small percentage (less than 5%) of the cells expressed PCNA. In cells cultured with rat PRL (10(-10)-10(-7) M) for 18 h, staining of PCNA increased in a dose-dependent manner, with maximal expression occurring at 10(-9) M PRL. At concentrations above 10(-9) M, PCNA staining decreased. To examine the specificity of the PRL-induced increase in PCNA, cells were incubated in the presences of 10(-9) M rat (r) or bovine (b) GH. Whereas incubation of astrocytes with rPRL and bPRL activated PCNA, cells incubated with either rGH or bGH showed only a slight increase in the number of cells expressing PCNA. Further, incubation of astrocytes with 1 nM PRL in the presence of 100 nM cyclosporine, an immunosuppressive agent that specifically displaces PRL from its receptor, decreased the percentage of nuclei stained for PCNA to that observed in non-PRL-stimulated controls. Transient exposure of cells to 10(-9) M PRL for 30 min resulted in an increase in the number of cells expressing PCNA when cultured for 18 h in the presence of 1% serum. In the presence of 1% serum, 10(-9) M PRL increased the incorporation of BrUd and resulted in a 3-fold increase in the doubling rate. In cells incubated in serum-free medium, only a few PCNA-positive cells could be detected. Treatment of Go-arrested astrocytes with PRL (10(-10)-10(-7) M) for 18 h resulted in a dose-dependent increase in the expression of PCNA. PCNA-positive cells were detected in cultures incubated with 10(-11) M PRL, with maximal expression at 10(-9) M.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Estradiol increases prolactin synthesis and prolactin messenger ribonucleic acid in selected brain regions in the hypophysectomized female rat.

Immunoreactive PRL which is not of pituitary origin, has been identified in many regions of the rat brain. We have previously demonstrated that estradiol increases hypothalamic immunoreactive PRL content in hypophysectomized female rats. To determine if estradiol stimulates PRL synthesis, we examined the effect of estradiol on the in vivo production of PRL, and on the expression of PRL messenger RNA (mRNA) in the hypothalamus, pons, and cerebral cortex. To examine the effect of estradiol on the in vivo production of PRL, [35S] methionine was injected into the lateral ventricle and its incorporation into immunoprecipitable PRL was determined by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In estradiol, but not vehicle-treated hypophysectomized rats, a 24,000 M(r) immunoprecipitable PRL protein was detected in the hypothalamus and pons-medulla, 2 and 4 h after methionine administration. No immunoprecipitable PRL proteins were detected in the amygdala, hippocampus, cortex, or serum at either time point. In addition, in the hypothalamus, but not the pons-medulla, a second PRL band was detected with an apparent mol wt of 16,000K. To determine if estradiol increased the expression of PRL mRNA, copy DNA was obtained by reverse transcription of poly(A+) mRNA prepared from intact and vehicle or estradiol-treated hypophysectomized rats and analyzed by polymerase chain reaction amplification. In tissues from hypophysectomized rats, there was little, or no, detectable levels of PRL mRNA. In contrast, in estradiol-treated hypophysectomized rats PRL mRNA was easily detected in the hypothalamus and pons-medulla by polymerase chain reaction amplification. These data suggest that estradiol increases the PRL content in the hypothalamus and pons-medulla by increasing PRL gene expression, in a manner similar to that reported in the pituitary.

Animals↗
PubMed1992

The metabolism of human sex hormone-binding globulin in the rhesus monkey.

The metabolism of human sex hormone-binding globulin (hSHBG) was studied in eight female rhesus monkeys (Macaca mulatta) after the pulse injection of [125I]-hSHBG. hSHBG was iodinated with 125I using a chloramine T technique, and the [125I]-hSHBG was separated from other constituents by molecular sieve chromatography with a Sephadex G-25 column. The [125I]-hSHBG was administered intravenously as a pulse in 2 ml of phosphate buffer, pH 7.4, to each of eight rhesus monkeys. Blood samples (2.0 ml) were obtained at 2, 4, 6, 8, 24, 30, 45, and 54 hr after the injection. The glycoproteins were precipitated with concanavalin A-Sepharose, and the radioactivity was measured. The concentration of radioactivity as fraction of dose/ml of serum was plotted on a semilog scale against time. The disappearance of radioactivity could be expressed best as the sum of two exponentials, with a mean +/- SE t1/2 of 2.5 +/- 0.4 and 33.1 +/- 3.7 hr, respectively. The initial volume of distribution was 461 +/- 78 ml and the metabolic clearance rate was 559 +/- 66 ml/day. The very low clearance rate and prolonged t1/2 are compatible with a relative stability in the circulating mass of SHBG. Rapid changes in concentration of SHBG could be due to changes in serum volume, reversible changes in tissue distribution of SHBG, or the secretion of variable forms of desialylated SHBG.

Animals↗
PubMed1991

Prolactin stimulation of protein kinase C activity in the rat hypothalamus.

Stimulation of cultured hypothalamic slices with PRL causes a rapid translocation of a Ca2+/phospholipid dependent protein kinase from the cytosol to the membrane fraction. The translocation of PKC from the cytosol to the membrane occurred at physiological concentrations of PRL with a maximal response occurring at 10(-10) M. At concentrations above this, there was less PKC activity translocated from the cytosol to the membrane. When injected into the medial preoptic area of the hypothalamus, PRL resulted in a similar translocation of PKC activity. These data clearly indicate that PRL can activate PKC in the rat hypothalamus, and suggest that PKC may be one of the transmembrane signaling mechanisms involved in the regulation of brain function by prolactin.

Animals↗
PubMed1991

Stimulation of hypothalamic prolactin release by veratridine and angiotensin II in the female rat: effect of ovariectomy and estradiol administration.

In the female rat immunoreactive prolactin (IR-PRL) has been identified in the hypothalamus and in other brain regions. Brain IR-PRL is not of pituitary origin and, based on polyacrylamide gel electrophoresis and peptide mapping, shares a high degree of sequence homology with its pituitary counterpart. We have previously shown that hypothalamic tissue can release IR-PRL in vitro when depolarized by potassium. In this study, we examined the release of IR-PRL from hypothalami obtained from intact and ovariectomized rats and incubated in the presence of veratridine (an alkaloid which depolarizes excitable membranes), angiotensin II, or thyrotropin-releasing hormone. Hypothalamic tissue spontaneously released IR-PRL, and this release was significantly increased by veratridine or angiotensin II in a dose-dependent manner. The specificity of the angiotensin-II-evoked IR-PRL release was demonstrated by the inhibitory effect of saralasin, an angiotensin II receptor antagonist, on hypothalamic IR-PRL release. Thyrotropin-releasing hormone (100 microM) had no effect on hypothalamic IR-PRL release. Ovariectomy decreased hypothalamic IR-PRL content and IR-PRL release in response to veratridine and angiotensin II. The effect of estradiol on hypothalamic IR-PRL content and release was also examined by obtaining hypothalami from ovariectomized rats injected with estradiol (1 microgram/day) or vehicle for 5 days. When compared with vehicle injected rats, administration of estradiol significantly increased the hypothalamic IR-PRL content (46 +/- 4 vs. 81 +/- 16 ng/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1989

Immunoreactive prolactin in the hypothalamus and cerebrospinal fluid of male and female rats.

Immunoreactive prolactin (ir-PRL) has been identified in the cerebrospinal fluid (CSF) and brain of the male and female rat. In this study we determined the concentration of ir-PRL in the CSF and hypothalamus under conditions known to increase or decrease serum PRL. Hypophysectomy (60 days) significantly decreased the concentration of ir-PRL in the CSF of male (4.9 +/- 0.7 vs. 3.0 +/- 0.3 ng/ml) and female (5.8 +/- 0.9 vs. 3.1 +/- 0.5 ng/ml) rats. However, the effect of long-term hypophysectomy on hypothalamic ir-PRL was gender-dependent. That is, in the male rat hypophysectomy did not affect the content of ir-PRL in the female rat, long-term hypophysectomy decreased the content of ir-PRL in the median eminence, ventral hypothalamus, and dorsal hypothalamus 37, 40, and 47%, respectively. Estradiol replacement to the hypophysectomized female rat normalized the content of ir-PRL in the median eminence (96 +/- 5.8 to 131 +/- 9.6 ng/mg protein), ventral hypothalamus (11 +/- 0.6 to 16.0 +/- 1.1 ng/mg protein), dorsal hypothalamus (4.7 +/- 0.4 to 8.6 +/- 0.4 ng/mg protein), and the concentration ir-PRL in the CSF (2.5 +/- 0.3 to 4.6 +/- 0.4 ng/ml). In intact female rats, administration of haloperidol induced a marked hyperprolactinemia, and significantly increased CSF ir-PRL (5.1 +/- 1.5 vs. 18.0 +/- 3.8 ng/ml). However, in the same rats, the content of ir-PRL in the median eminence was significantly decreased while the ir-PRL content in the ventral hypothalamus and dorsal hypothalamus was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Thyrotropin (TSH)-releasing hormone-stimulated TSH release and TSH concentration in the guinea pig pituitary, as determined by a heterologous radioimmunoassay.

Little is known regarding how the guinea pig (GP) compares with the rat in terms of TSH economy. To develop a heterologous RIA for GP TSH, rabbits were injected with GP TSH. In one rabbit (anti-gpTSH-8), antibodies that bound 125I-labeled bovine (b) TSH and rat (r) TSH but not 125I-labeled bLH or rPRL were generated. The binding of anti-gpTSH-8 to [125I]bTSH was inhibited in a parallel manner by bTSH over a range of 0.047-5.42 ng, rTSH over a range of 0.24-25 ng, and dilutions of GP pituitary extracts. This system, with bTSH as the standard, was employed as the basis for a heterologous TSH RIA (GP TSH RIA). The cross-reactions of rTSH and bLH in the GP TSH RIA were 45% and 7%, respectively. Rat and bovine FSH, GH, and PRL had little or no cross-reaction. GP pituitaries were incubated in vitro and dosed with LHRH and TRH. The GP TSH RIA detected an 11-fold increase in TSH in the medium in response to TRH and no change in immunoreactivity in response to LHRH. In contrast, a RIA for bLH detected a 25-fold increase in LH in the medium in response to LHRH and no increase in response to TRH. The TSH content in GP pituitaries was significantly lower than that in the rat (GP, 16.8 +/- 1.6 ng/mg; rat, 80.3 +/- 6.2 ng/mg; P less than 0.05) as were serum TSH concentrations (GP, 0.8 +/- 0.4 ng/ml; rat, 4.5 +/- 1.1 ng/ml; P less than 0.05). Thyroid hormone administration (T4 Rx) in both GP and rat produced a significant reduction in pituitary TSH content (GP control, 4.8 +/- 0.4 ng/mg; T4 Rx, 2.1 ng/mg; P less than 0.05; rat control, 52.4 +/- 4.0 ng/mg; T4 Rx, 20.5 +/- 1.6 ng/mg; P less than 0.05) and TSH release (GP control, 9.4 +/- 2.3 ng/ml; T4 Rx, 4.3 +/- 1.5 ng/ml; P less than 0.05; rat control, 357 +/- 81 ng/ml; T4 Rx, 133 +/- 27 ng/ml; P less than 0.05) from incubated hemipituitaries. Thyroidectomy in the rat was associated with a decrease in pituitary TSH content, but no change in pituitary content was found in thyroidectomized GPs. These studies demonstrate the feasibility of estimating GP TSH with a heterologous RIA that employs polyvalent antiserum against GP TSH as the first antibody and bTSH as the tracer and standard.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Serum thyrotropin concentrations are more highly correlated with serum triiodothyronine concentrations than with serum thyroxine concentrations in thyroid hormone-infused thyroidectomized rats.

To assess the relative role of circulating T4 and T3 in the regulation of serum TSH, we have measured serum T4, T3, and TSH concentrations in normal and thyroidectomized rats, some of which were chronically infused with T3 or T4. Serum T3, T4, and TSH concentrations were measured 7 and 14 days after surgery. Some groups of infused rats were mildly hypothyroid, as judged by elevated serum TSH concentrations. At both 7 and 14 days, there was a significant inverse correlation between serum T3 and serum TSH concentrations (day 7, r = 0.65, P less than 0.01; day 14, r = 0.71, P less than 0.01). The coefficients for the inverse correlations between serum T4 and TSH concentrations were 0.37 on day 7 (P less than 0.05) and 0.37 (P less than 0.05) on day 14. Linear regression analysis was performed using TSH as the dependent variable for outcome and serum T3 and T4 concentrations as the independent predictor variables. This analysis revealed that after controlling for T3, TSH and T4 were no longer significantly correlated (P = 0.14). The correlation between T3 and TSH remained highly significant. These results suggest that in the euthyroid and mildly hypothyroid rat, serum T3 has a greater inhibitory effect on TSH secretion than does serum T4.

Animals↗
PubMed1989

Fasting-associated changes in serum thyrotropin in the rat are influenced by gender.

Studies in the male rat have demonstrated that fasting is associated with a decrease in serum TSH concentrations. The present studies were performed to determine if gender influenced the serum TSH changes associated with fasting. In 8 of 10 experiments in male rats, serum TSH concentrations were significantly reduced in fasted compared to fed groups. In contrast, in none of the 9 experiments in female rats were serum TSH concentrations significantly reduced in the fasted groups. When all experiments were pooled, the decrease in the serum TSH concentration in the fasted rats compared to that in the fed rats was 55 +/- 4% (mean +/- SE) in males and 10 +/- 7% in females (P less than 0.001). In female rats ovariectomy did not result in a pattern in which fasting was associated with a decrease in serum TSH concentrations. Testosterone (T) was administered to male rats during fasting, but this treatment did not prevent the fasting-induced decrease in serum TSH concentrations. In gonadectomized male rats serum TSH concentrations were unchanged by fasting. However, if T was administered to gonadectomized male rats before and during fasting, serum TSH concentrations were significantly decreased in the fasted compared to the fed rats. These studies indicate that there is a sex difference in the serum TSH response to fasting in rats. The decline in serum TSH with fasting in the male rat is not mediated by a decline in serum T concentrations. Rather, T appears to maintain a process which increases the serum TSH concentration, and it is this process that is susceptible to inhibition by fasting.

Animals↗
PubMed1989

Thyroid hormone regulation of hypothalamic immunoreactive thyrotropin.

Immunoreactive TSH (IR-TSH) has been identified in the hypothalamus and other brain areas in intact and hypophysectomized rats. To determine if thyroid hormones regulate IR-TSH in the rat brain, the effects of T3 and T4 on pituitary and hypothalamic IR-TSH content were studied in intact and hypophysectomized rats. Female rats received daily injections of T3 (0.1, 1.0, or 10 micrograms/100 g BW) or T4 (0.5, 2.5, or 5.0 micrograms/100 g BW) for 7 days. The chronic administration of T3 and T4 decreased the plasma concentration and pituitary content of IR-TSH in a dose-dependent manner. In intact rats, the administration of T3 did not affect the content of IR-TSH in the median eminence, ventral hypothalamus, or dorsal hypothalamus. In contrast, administration of T4 significantly increased the content of IR-TSH in the median eminence and ventral hypothalamus in a dose-dependent manner. Similarly, in hypophysectomized rats daily administration of T4 resulted in a dose-dependent increase in the concentration of IR-TSH in the median eminence and ventral hypothalamus. In hypophysectomized rats infusion of colchicine into the lateral ventricle, which blocks axonal transport, decreased the content of IR-TSH in the median eminence (631 +/- 59 vs. 439 +/- 36 microU/mg), increased the content of IR-TSH in the ventral hypothalamus (45 +/- 5 vs. 87 +/- 10 microU/mg), and blocked the T4-induced increase in IR-TSH in the median eminence. In intact rats, administration of iopanoic acid, which blocks the conversion of T4 to T3, decreased the content of IR-TSH in the median eminence (688 +/- 44 vs. 450 +/- 38 microU/mg) and ventral hypothalamus (103 +/- 16 vs. 70 +/- 5 microU/mg) and blocked the T4-induced increase in IR-TSH in the median eminence (1025 +/- 82 vs. 644 +/- 62 microU/mg) and ventral hypothalamus (229 +/- 23 vs. 117 +/- 11 microU/mg). These data indicate that TSH content in the median eminence and ventral hypothalamus is regulated by a thyroid hormone-sensitive mechanism which requires the local monodeiodination of T4 to T3. In addition, the effect of colchicine on the IR-TSH content in the median eminence and the T4-induced increase in brain IR-TSH are consistent with previous reports demonstrating that hypothalamic IR-TSH is regulated independently of pituitary and serum TSH.

Animals↗
PubMed1989

Comparison of brain and pituitary immunoreactive prolactin by peptide mapping and lectin affinity chromatography.

Immunoreactive PRL (IR-PRL) has been identified in many areas of the rat brain. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyses we have recently shown that the primary IR-PRL protein in the rat brain has an apparent mol wt (Mr) of 24,000, which was identical to that of pituitary PRL. In these studies, brain and pituitary 24,000 Mr PRL were compared by peptide mapping and lectin chromatography. PRL-enriched fractions were prepared from the pituitary, hypothalamus, hippocampus, and pons-medulla and labeled with 125I. This material was further purified by immunoprecipitation, and immunopurified 24,000 Mr PRL was isolated by sodium dodecyl sulfate-gel electrophoresis. Cleavage of 125I-labeled 24,000 Mr IR-PRL prepared from the pituitary and the three brain regions with chymotrypsin resulted in identical peptide maps with two primary labeled peptide fragments (5,500 and 6,000 Mr), and approximately five less intense fragments. Similarly, trypsin cleavage of brain and pituitary 24,000 Mr IR-PRL resulted in the production of two major fragments (6,200, and 5,200 Mr), and three less intense fragments. Cleavage of the 24,000 Mr IR-PRL with Staphylococcus V8 protease resulted in identical fragment patterns with two primary peptide fragments (14,000 and 6,200 Mr). When the pituitary and brain 24,000 Mr PRL were applied to Concanavalin-A-Sepharose columns no 24,000 Mr PRL was absorbed. The similarity of the peptide fragments obtained from the cleavage of the 24,000 Mr IR-PRL from the brain and pituitary clearly indicate that the IR-PRL found in the brain has an amino acid sequence that shares a high degree of structural homology with pituitary PRL.

Animals↗
PubMed1988

Heterogeneity of immunoreactive prolactin in the rat brain.

Three immunoreactive prolactin proteins (24 Kd, 16 Kd, and 12 Kd) were identified in the rat brain using sodium dodecyl sulphate polyacrylamide gel electrophoresis, and western blot analyses. In male and female brains, the primary prolactin protein has a molecular weight of 24 Kd which is similar to that of pituitary prolactin. Two additional proteins with apparent molecular weights of 16 Kd and 12 Kd were also identified and were found in greater concentrations in the brain than in the pituitary, and were more predominant in the female brain. In addition, brain extracts proteolytically modify the 24K dalton PRL resulting in the formation of two fragments with apparent molecular weights of 16 and 8 Kd. These data indicate that the prolactin identified in the rat brain is similar to pituitary prolactin, and suggests, that like other PRL target tissues the brain may have the capacity to proteolytically modify prolactin.

Animals↗
PubMed1988

Distribution of immunoreactive prolactin in the male and female rat brain: effects of hypophysectomy and intraventricular administration of colchicine.

Immunohistochemical studies have identified immunoreactive prolactin (IR-PRL) in the hypothalamus and other areas of the rat brain. However, immunocytochemical techniques make it difficult to quantify the amount of antigen localized in a specific region. In this study, IR-PRL was extracted from selected regions of the rat brain, consisting of the median eminence, dorsal and ventral hypothalamus, thalamus, amygdalae, cerebellum, cortex, hippocampus, septum, pons-medulla, and olfactory lobes, and the concentrations of IR-PRL were determined by radioimmunoassay. Whereas IR-PRL was detected in all brain regions in both the male and the female rat brain, the concentrations of IR-PRL in the female rat were significantly greater than those measured in the corresponding region of the male rat brain. In the female rat, hypophysectomy significantly reduced, but did not eliminate, the concentration of IR-PRL in hypothalamus, amygdala, thalamus, and pons-medulla. In contrast, hypophysectomy did not affect the concentration of IR-PRL in any brain regions of the male rat. Injection of colchicine into the lateral ventricle decreased the concentration of IR-PRL in the median eminence and increased the concentration of IR-PRL in the ventral hypothalamus in male and female rats. In addition, extracted hypothalamic and pituitary IR-PRL displayed similar dilution curves in the PRL assay and elution patterns on Sephadex G-100. These data indicate that both the male and the female rat brain contains an IR-PRL-like material with physicochemical properties similar to those of pituitary PRL. This material is differentially distributed in the male and female brain and is found in greater concentrations in the female brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Immunoreactive prolactin in the rat hypothalamus: in vitro release and subcellular localization.

Immunocytochemical studies have identified immunoreactive prolactin (IR-PRL) in the hypothalamus and other areas of the rat brain. However, neither the release of IR-PRL from the hypothalamus nor its subcellular localization have been demonstrated. In this study, the release of IR-PRL from hypothalami obtained from female rats was examined using hypothalamic units incubated in vitro in Krebs-Ringer bicarbonate-glucose buffer. Hypothalamic tissue spontaneously released IR-PRL, and this release was increased by depolarizing concentrations of potassium by a calcium-dependent mechanism. Hypothalamic IR-PRL was also released from hypothalamic tissue obtained from hypophysectomized rats (14 days). The subcellular localization of IR-PRL was investigated using equilibrium-density centrifugation. Tissue homogenates from intact or hypophysectomized rats were centrifuged at 150 g at 4 degrees C for 10 min, and the supernatants were layered onto continuous sucrose gradients (1.00-1.27 g/ml) and centrifuged at 100,000 g (max.) for 16 h. IR-PRL in pituitary supernatants showed a high equilibrium-density peak with a modal density of 1.23 g/ml. Fractionation of the supernatant from ventral or dorsal hypothalamic tissue resulted in two high-equilibrium density peaks, a primary peak with a modal density of 1.23 g/ml and a smaller peak with a modal density of 1.10 g/ml. Both high-density peaks were maintained in tissue obtained from hypophysectomized rats and were disrupted by homogenization in hypo-osmotic medium. Together, these data suggest that hypothalamic IR-PRL is stored in membrane-bound particles which have densities similar to those of secretory granules and is released by a calcium-dependent mechanism when the tissue is depolarized.

Animals↗
PubMed1987

The pituitary TSH response to TRH is inversely related to the plasma TSH concentration and directly related to the pituitary TSH content during hypothyroidism in the rat.

We studied the effects of degree and duration of hypothyroidism on the pituitary TSH concentration and the pituitary TSH secretory response to TRH. Varying degrees of hypothyroidism were achieved in thyroparathyroidectomized rats (THYREX) by continuous sc infusion of T3 (0.2, 0.3, 0.4, or 0.5 microgram/100 g X day) or T4 (0.6, 1.2, or 1.8 microgram/100 g X day). While T3 was more potent than T4, both resulted in a dose-dependent suppression of the post-thyroidectomy rise in TSH. After 7 or 14 days of severe hypothyroidism (nonreplaced THYREX rats) the pituitary TSH secretory response to TRH (250 ng/100 g body weight, iv) was found to be decreased when compared to that of euthyroid rats. Decreasing the degree of hypothyroidism increased the pituitary secretory response to TRH and the pituitary TSH content. The results indicate that in the hypothyroid rat: severe hypothyroidism results in a blunted pituitary TSH response to TRH through 14 days after thyroidectomy, at 7 and 14 days after thyroidectomy the pituitary TSH response to exogenous TRH is inversely related to the basal plasma TSH concentration, the pituitary TSH concentration increases with the duration of hypothyroidism, the pituitary TSH content is increased by low rates of thyroid hormone replacement, and the pituitary TSH response to exogenous TRH is directly related to the pituitary TSH content.

Animals↗
PubMed1986

Subcellular localization of immunoreactive thyroid-stimulating hormone in the rat hypothalamus.

Hypothalamic tissue contains TSH-like material which is biologically, immunologically, and physicochemically similar to pituitary TSH. Immunoreactive thyroid-stimulating hormone (IR-TSH) is released from hypothalamic tissue in vitro by depolarizing concentrations of potassium or veratridine by a calcium-dependent mechanism. In the present study, we investigated the subcellular localization of IR-TSH using equilibrium density centrifugation. Tissue homogenates from intact, hypophysectomized or thyroidectomized rats were centrifuged at 150 g at 4 degrees C for 10 min and the supernatants were layered onto continuous sucrose gradients (1.00-1.27 g/ml) and centrifuged at 100,000 g (max) for 16 h. IR-TSH in pituitary supernatants from intact and thyroidectomized rats showed high equilibrium density peaks with a modal density around 1.2 g/ml. Fractionation of the supernatant from ventral or dorsal hypothalamic homogenates resulted in a bimodal distribution of IR-TSH. In supernatants from both tissues, IR-TSH containing particles were found at the top of the gradient in a low equilibrium density peak between 1.0 and 1.08 g/ml. In addition, IR-TSH containing particles were found in ventral and dorsal hypothalamic supernatants with modal densities at 1.16 and 1.25, respectively. These high density IR-TSH particles were present in tissue taken from hypophysectomized rats, and were not appreciably affected by thyroidectomy. Homogenization of the tissue in a hypo-osmotic medium disrupted the high density IR-TSH particles resulting in a single low density peak at the top of the gradient. These data suggest that hypothalamic IR-TSH is stored in membrane bound particles which have densities similar to that of secretory granules.

Animals↗