ACTH determination in a petrosal sinus venous specimen after corticotrophin releasing factor provides the best clue on the laterality of microadenoma in Cushing's disease

A 42-year-old woman with Cushing's disease was endocrinologically cured after transsphenoidal selective excision of a left-sided microadenoma. Simultaneous samplings from the bilateral inferior petrosal sinuses with ovine corticotrophin-releasing factor (CRF) stimulation were performed preoperatively to evaluate some relations between the localization of a possible microadenoma and the levels of ACTH in inferior petrosal sinuses. The data for the venous samplings were as follows:-(1) The basal levels of ACTH obtained simultaneously from both inferior petrosal sinuses and peripheral vein were about the same. (2) A significant difference, with a high level of ACTH from the ipsilateral side of the microadenoma, was demonstrated after CRF stimulation. (3) The magnitude of increase in ACTH on the contralateral side after CRF was similar to that of the peripheral response. It is recommended that all patients with ACTH dependent Cushing's syndrome and negative radiological findings should have bilateral simultaneous inferior petrosal venous sampling with CRF stimulation.     

Mechanisms of insulin degradation by isolated rat adipocytes

Summary We have examined some of the chemical and biological characteristics of the insulin-derived cell-associated radioactivity following incubation of isolated adipocytes with ¹²⁵I-insulin (10^–10 M) for one hour at 37 °C S ephadex G-50 chromatography of the cell-associated radioactivity demonstrated three peaks: peak I eluted with the void volume and consisted of large molecular weight material; peak II comigrated with 1251-insulin; and peak III consisted of small molecular weight degradation products (probably iodotyrosine). When the insulin peak (peak II) was divided into fourths, it was found that the binding and biologic activity of this material was not homogenous; thus, binding and biologic activity (relative to native insulin) fell markedly from the earliest to the latest eluting fractions of this peak. Furthermore, when the entire peak 11 material was applied to DEAE-Sephacel and eluted with a 0.01–0.2 M NaCl gradient, three distinct peaks were observed. These peaks were all 90% TCA precipitable, whereas the ability of the latter two eluting peaks to precipitate with anti-insulin antiserum was markedly reduced. When similar experiments were performed with chloroquine-treated cells, a large increase in cell-associated radioactivity was observed, and Sephadex G-50 chromatography demonstrated that this increase was entirely confined to peaks I and II. When the insulin peak (peak II) was divided into fourths, it was found that chloroquine markedly inhibited the decreased binding and biologic activity, from the earliest to the latest eluting fraction of this peak. Furthermore, when the peak II material (Sephadex G-50) from chloroquine-treated cells was chromatographed on DEAE-Sephacel, this material eluted in a single peak which was 95% TCA precipitable and 106% precipitable by anti-insulin antiserum. In conclusion, these studies demonstrate that: 1) intermediate insulin-derived products with reduced binding and biologic activity are generated in the process of cellular insulin degradation, and 2) the formation of these intermediate products is mediated by a chloroquine-sensitive pathway.     

The corpus luteum of the pig. Scanning electron microscopic study of surface features at different times of incubation

The surface ultrastructure of porcine early corpus luteum cells (days 1-3 of the luteal phase) was studied in SEM and correlated with progesterone secretion. Luteal cells were divided into 2 groups: small cells (10-20 microns) and large cells (20-30 microns) and their surface features were observed after 1, 3, and 5 h of incubation in the control medium and in a medium supplemented with prolactin (PRL). The surface morphology of control cells was characterized by numerous smooth blebs and the presence or absence of thin microvilli. Small and large cells showed a tendency to adhere to the glass during the experiment, but on the large cells the number of thin adhesive filopodia was greater. After the 1st and 3rd h of incubation with PRL the number of microvilli and numerous filopodia on the small cells increased substantially. Nodular blebs were scattered and appeared to protrude from the cell surface. Many small cells adhered to the glass by thick, layered and thin thread-like cytoplasmic processes. After the 5th h distinct smoothing of the surface of the small cells was seen. The number of microvilli seen on the PRL stimulated surface of the large cells was smaller and in some cases even entirely absent. After the 1st and 3rd h of the experiment the large cell surface was ruffled with minute folds. Numerous nodular blebs protruded from the cell surface. The number of adhesive filopodia attaching the cells to the glass decreased or vanished during the experiment. After the 5 h of incubation most of the cells had smooth surface with smooth blebs. Progesterone secretion was measured by radioimmunoassay. The cells in the medium without exogenous hormone (control) secreted relatively low levels of progesterone throughout 1-5 h of the incubation period. After addition of PRL to the medium the amount of secreted progesterone increased.     

Biochemical and Molecular Responses to Loss of Renal Mass: Atpase and Cyclic Nucleotides: Evidence for Altered Cyclic Nucleotide Metabolism During Compensatory Renal Hypertrophy and Neonatal Kidney Growth

In adult male Sprague-Dawley rats contralateral nephrectomy was followed by an initial fall of the concentration of cGMP in renal cortical tissue followed by a rise to a peak level of 300 percent of the initial concentration within two hours. cGMP concentration in the remaining renal cortex remained at about 300 percent of the initial value during the subsequent 72 hours and slowly declined to 150-200 percent in the following two weeks. The changes in cGMP concentration were due to exactly parallel changes in the soluble fraction of renal cortical guanylate cyclase activity, while cGMP-phosphodiesterase activity remained unchanged. cAMP concentration after contralateral nephrectomy fell significantly by about 25 percent within two hours and remained below baseline level for up to eight hours. In the kidneys of newborn rats the concentration of cAMP was approximately one-half that found in adult kidneys: it slightly fell between the fourth and the seventh day after birth and subsequently continuously rose to reach adult values approximately two weeks after birth. The concentration of cGMP was significantly greater four days after birth than in adult rats, further rose between the fourth and the seventh day after birth and subsequently gradually declined to adult levels. The increased cGMP concentration appears to be due to an increase of guanylate cyclase activity in total kidney homogenates which, in turn, was mainly due to an increase of the particulate (membrane-bound) fraction of the enzyme. cGMP-phosphodiesterase activity, however, was also increased in respect to adult levels, one or three weeks after birth. Renal growth from the seventh day after birth to adulthood is accompanied by a continuous increase of the ratio cAMP/cGMP. Removal of one kidney four to seven days after birth resulted in a slower increase of this ratio. The data suggest that cGMP may trigger renal growth and that increases of cGMP concentration in the kidneys are the result of a primary increase in the activity of guanylate cyclase.     

Ovulation in light-estrous rats induced by darkness

Adult female rats show continual vaginal cornification and cease ovulation a few weeks after they are exposed to continuous lighting (light-estrous rats). When these rats were placed in the darkness for 10 hr, 80% of the animal ovulated approximately 46 hr later. Peripheral LH increased to a small peak immediately after placing in darkness concomitant with a decrease in pituitary LH content; a large peak, 20 times higher than the basal LH level, was observed at 20 to 22 hr. Progesterone concentration in ovarian vein blood remained at extremely low levels while estrogen levels tended to rise after small LH peak. This estrogen rise appeared to play an important role in inducing the main LH peak. Simulation of the small LH peak by low doses of exogenous LH succeeded in inducing ovulation of light-estrous rats in similar fashion to the exposure of light-estrous rats to 10-hr darkness. Therefore, the small amount of LH secretion observed after the initiation of the darkness-treatment may be considered as a trigger for the whole sequence of hormonal changes leading to ovulation.     

Endocrine regulations of reproductive seasonality, follicular development and incubation in Magang geese

This study investigated the regulatory mechanisms of seasonal breeding, developments of ovarian follicles and incubation in Magang geese, a short day breeding bird. Throughout the year, plasma PRL concentrations increased in non-breeding season in spring and summer (from April to early August), and remained low in the rest of the year, while LH concentrations peaked in August and September and remained low in non-breeding season (March to June). Lengthening photoperiod increased PRL and decreased LH secretions, which inhibited follicular development, terminated lay and induced moulting, while shortening photoperiod decreased PRL and increased LH secretion and reinitiated lay. Long photoperiod stimulated PRL secretion occurred with increased gene expressions of PRL in the pituitary gland and VIP in the hypothalamus, but inhibition of LH secretion was without decreases in gene expressions of LH beta subunit and GnRH. Under breeding conditions, terminating incubation decreased PRL but increased LH concentrations and resumed lay in 24 days following recruitment of about 10 large white follicles into hierarchical development. Plasma concentrations of progesterone and inhibin peaked at peak lay, whereas LH concentrations exhibited a bi-phasic pattern with troughs at peak lay and incubation when PRL concentrations were high. Ninety percent geese exhibited incubation behaviour after laying one clutch of approximately eight eggs in approximately 30 days. In conclusion the seasonal reproductive activities in Magang geese is directly inhibited by long photoperiod and directly stimulated by short photoperiod via PRL and LH secretions, whose interplays also cause occurrences of four to five lay and incubation cycles in the breeding season.     

Stimulatory effect of oCRH on alpha-subunit secretion during petrosal sinus sampling in patients with Cushing's disease.

During bilateral and simultaneous venous sampling of the inferior petrosal sinuses for preoperative localization of ACTH secreting microadenomas, alpha-subunit levels, in addition to ACTH, were determined in 9 patients with Cushing's disease. The aim of the study was to evaluate the possible occurrence of unilateral increases of alpha-subunit in basal conditions and the alpha-subunit responsiveness to oCRH. All the patients examined showed a central to peripheral and an intersinus gradient of ACTH concentrations before and/or after oCRH stimulation. Seven patients showed a central to peripheral alpha-subunit gradient in basal conditions. Lateralization of alpha-subunit concentrations was recorded in 4 patients in basal conditions (intersinus gradient > or = 1.55) and paralleled the side with the highest ACTH concentrations. After oCRH stimulation all but one patient showed a unilateral alpha-subunit increase in blood from the inferior petrosal sinus with the highest oCRH stimulated ACTH increase. The present data confirm the occurrence of an increase of alpha-subunit concentration in response to nonspecific stimulation with exogenously administered oCRH, concurrent with an ipsilateral increase of ACTH levels. The mechanism underlying this finding is still unclear, although a paracrine effect from the corticotroph tumour on adjacent pituitary tissue seems so far the most likely explanation.     

Ectopic ACTH syndrome

Ectopic ACTH syndrome represents a cancer-induced amplification of a property [proopiomelanocortin (POMC) peptides production] normally present in the cells from which the cancer originated but with aberrant posttranslational processing of POMC resulting in a greatly elevated secretion of ACTH precursors. The classic ectopic ACTH-producing tumors described in the 1960s were highly malignant but more recently slowly growing tumors such as carcinoids are reported with increasing frequency. Clinical features of patients with ectopic ACTH were analyzed, including biochemical abnormalities, plasma ACTH, cortisol and urinary steroids. Dynamic tests such as high-dose dexamethasone suppression, metyrapone and ovine-CRH (oCRH) stimulation were explored, as well as inferior petrosal sinus ACTH sampling before and after oCRH. Among the tumor markers examined, elevation of ACTH precursors was uniformly present followed by increased output of calcitonin, gut hormones, oncofetal and placental hormones in decreasing order. Since more than 90% of ectopic ACTH tumors are neuroendocrine in nature exhibiting APUD characteristics, their 2 markers, neuron-specific enolase and chromogranins are very useful. The imaging procedures for localization of the tumor ranged from chest X-rays to computed tomography and magnetic resonance of the chest and abdomen. Abdominal ultrasonography was also useful. Finally somatostatin receptor scintigraphy permitted demonstration of unrecognized tumors and/or metastases, even when the tumors were occult. The ACTH content, immunostaining for APUD markers and altered POMC processing were evaluated in ectopic tumors and/or metastases. Occult ectopic ACTH syndrome of more than 4–6 months of symptoms without the emergence of an obvious source was reviewed. Since the tumors are often clinically and biochemically undistinguishable from pituitary-dependent Cushing's disease, inferior petrosal sinus sampling for ACTH after oCRH stimulation established the diagnosis in over 90% of the cases. 60% of the occult tumors were thoracic carcinoids (3/4 bronchial carcinoids), followed by small cell lung cancer and pancreatic neuroendocrine tumors. In 12% the primary etiology was not detected. The rare syndrome of ectopic CRH syndrome (6 published cases) leading to excessive stimulation of the pituitary which became hyperplastic and secreted excessive amounts of ACTH is discussed. Finally, the 12 published cases and 1 unreported patient with ectopic CRH-ACTH tumors were reviewed, the majority being metastatic small cell lung carcinomas, bronchial and thymic carcinoids.     

Transforming growth factor beta 1 and adrenocorticotropin differentially regulate the synthesis of adrenocortical cell heparan sulfate proteoglycans and their binding of basic fibroblast growth factor.

Adrenocortical differentiated functions are under the control of both endocrine hormones such as ACTH and local factors such as transforming growth factor beta (TGF beta) or basic fibroblast growth factor (bFGF). Besides their regulatory actions on the synthesis of corticosteroids, these two classes of factors also exert some important effects on the cellular environment. We have examined here the regulation by ACTH and TGF beta of adrenocortical cell proteoglycan synthesis and secretion. Under basal conditions, adrenocortical cells synthesized and secreted several species of sulfated proteoglycans, 80% of them being recovered in solution in the culture medium. When analyzed by ion exchange chromatography, the cell extracts and the media from cells metabolically labeled with 35S-sulfate were found to contain two and three species of radioactive sulfated proteoglycans, respectively. All species were proteoheparan-sulfates. Treatment of adrenocortical cells with TGF beta 1 or ACTH resulted in a significant increase of the incorporation of 35S into both secreted and cell-associated proteoglycans. ACTH stimulated more than three times the amount of secreted proteoglycans eluting from DEAE-Trisacryl as peak B, whereas TGF beta preferentially increased the amount of peak C. No important modification of the size of the synthesized proteoglycans was observed. The subpopulation of heparan sulfate proteoglycans capable to bind bFGF was also largely increased after ACTH or TGF beta treatment and paralleled the variation in overall proteoheparan sulfate synthesis. Thus those effects of TGF beta and ACTH on proteoglycan synthesis may participate in an increased ability of adrenocortical cells to bind and respond to bFGF.     

Detailed profile of prolactin secretion in the immature female rat: evidence for the existence of an ultradian rhythm

The detailed profile of prolactin (PRL) secretion in 22-24 and 29-31 days old female rats was investigated by serial blood sampling through an intracardiac cannula at 15-min intervals for each of the 9 or 10-h periods beginning at 09.00 or 10.00 and 22.00 h. By analysis of the power spectrum and the least squares method the time series of PRL concentrations which were measured by RIA were found to have approximately a 3-h period ultradian rhythm in either sampling period of both the 22-24 and 29-31 days old rats. The peak times calculated based on the acrophase estimated through the calculation of periodicity were concentrated around 12.00, 15.00 and 18.00 h for the sampling period 10.00-19.00, and 24.00, 03.00 and 06.00 h for the sampling period 22.00-07.00 h. However, in more than half of the animals at 22-24 days of age, one secretory episode around 12.00 h, and two secretory episodes around 24.00 and 03.00 h had markedly small amplitudes, making the remaining secretory episodes distinct diurnal and nocturnal surges, respectively. In the animals at 29-31 days of age, the amplitudes of the PRL episodes occurring around 12.00 h were markedly small, making the remaining two episodes as diurnal surges, whereas the amplitudes of PRL secretory episodes during the period 22.00-07.00 h were analogous to each other. These findings indicate that the semicircadian rhythm of PRL secretion is established on the basis of PRL secretion with the 3.0-h period ultradian rhythm.     

Cyclic AMP-dependent protein kinase isoenzymes in human myeloid leukemia (HL60) and breast tumor (MCF-7) cells

Combinations of retinoic acid (RA) and cAMP mediate many biological responses in a large variety of cell types. While the basis for the apparent synergistic effects of RA and cAMP are not clearly defined, it is likely that activation of PKA by cAMP is involved. However, literature reports concerning the identity of PKA isoforms in HL60 and MCF-7 cells are conflicting. The purpose of the present investigation is to identify PKA isoforms in HL60 and MCF-7 cells. Utilization of high-performance anion-exchange liquid chromatography, immunoblotting, and 8-azido-cAMP photoaffinity binding resulted in the finding that HL60 cells contain PKA types I alpha and II alpha, while MCF-7 cells contain PKA types I alpha, II alpha, and II beta. PKA type I alpha in both HL60 and MCF-7 cells eluted from columns as two well-separated peaks. One peak eluted at a low salt concentration in agreement with previous reports. The second HL60 PKA type I alpha peak eluted at a salt concentration intermediate between that eluting the first peak and that eluting PKA type II alpha and contained approximately 62% of the total RI alpha protein. However, the second MCF-7 PKA type I alpha peak contained approximately 66% of the total RI alpha protein and co-eluted with PKA types II alpha and II beta. This "contamination" of PKA type II fractions with PKA type I has led, in some cases, to interpretations that may need reevaluation.     

Measurement of pulsatile insulin secretion in the rat: direct sampling from the hepatic portal vein

It has previously been shown that insulin is secreted in discrete secretory bursts by sampling directly from the portal vein in the dog and humans. Deficient pulsatile insulin secretion is the basis for impaired insulin secretion in type 2 diabetes. However, while novel genetically modified disease models of diabetes are being developed in rodents, no validated method for quantifying pulsatile insulin secretion has been established for rodents. To address this we 1) developed a novel rat model with chronically implanted portal vein catheters, 2) established the parameters to permit deconvolution of portal vein insulin concentrations profiles to measure insulin secretion and resolve its pulsatile components, and 3) measured total and pulsatile insulin secretion compared with that in the dog, the species in which this sampling and deconvolution approach was validated for quantifying pulsatile insulin secretion. In rats, portal vein catheter patency and function were maintained for periods up to 2-3 wk with no postoperative complications such as catheter tract infection. Rat portal vein insulin concentration profiles in the fasting state revealed distinct insulin oscillations with a periodicity of approximately 5 min and an amplitude of up to 600 pmol/l, which was remarkably similar to that in the dogs and in humans. Deconvolution analysis of portal vein insulin concentrations revealed that the majority of insulin ( approximately 70%) in the rat is secreted in distinct insulin pulses occurring at approximately 5-min intervals. This model therefore permits direct accurate measurements of pulsatile insulin secretion in a relatively inexpensive animal. With increased introduction of genetically modified rat models will be an important tool in elucidating the underlying mechanisms of impaired pulsatile insulin secretion in diabetes.     

Prolactin secretion in cattle as affected by haloperidol and α-Methyl-p-Tyrosine

Prolactin (PRL) secretion in response to i.v. injection of different doses of α-Methyl-p-Tyrosine (αMT) and haloperidol (HAL) was studied in one cow and three bulls. HAL was tested at doses of 0.033, 0.1, and 0.33 mg/kg body weight (BW), and αMT was tested at doses of 0.1, 1.0, 10, and 30 mg/kg BW. Blood was collected via an indwelling catheter into the external jugular vein, and plasma PRL was analysed by radioimmunoassay. Dose-related increases in plasma PRL concentrations were observed after administration of both αMT and HAL. Peak PRL concentrations after injection of HAL at a low, medium, and high dose were 22, 45, and 70 ng/ml, respectively. Peak PRL concentrations after injection of increasing doses of αMT were 3.0, 10, 40 and 70 ng/ml. HAL (0.1 mg/kg BW) and αMT (10 mg/kg BW) were administered intravenously to four heifers during summer and winter. Response to both drugs, as measured by changes in PRL secretion, was greater in summer than winter. Peak plasma PRL levels after HAL injection were 327 ± 58 ng/ml in June and 149 ± 27 ng/ml in January, whereas peak levels after αMT were 166±29 and 60±9 ng/ml, respectively. Basal PRL secretion was also greater in summer than winter. The results of this study demonstrate that PRL in peripheral plasma of cattle is increased in response to administration of antidopaminergic drugs and that this increase is greater during the summer than the winter.     

Naloxone injected into the preoptic region has hypophysiotropic and seizurogenic actions in rats.

The effects of microinjection of naloxone, an opiate receptor antagonist, into the medial preoptic area (MPO) and diagonal band of Broca (DBB) on luteinizing hormone (LH) and prolactin (PRL) secretion were examined in the intact male rat and female rat in diestrus 1. In both the male and female rats, the injection of 50 micrograms naloxone at 1300 h produced an acute, two- to three-fold increase in serum LH, attaining the peak at 20 min. The PRL concentration in the female 20 min-2 h after the injection was significantly lower than in the saline-injected rat. In the male rat, naloxone caused a decrease in the PRL concentration in the late afternoon when a small rise occurred in the saline-injected rat, although it caused no immediate changes. In addition to these hypophysiotropic effects, naloxone injected in the MPO and DBB unexpectedly had seizurogenic actions. More than 40% of the animals of both sexes given an injection of naloxone had behavioral seizures, which began after about 20 min and were repeated intermittently at 15-20 min intervals through the sampling period of 6 h. In the LH and PRL response to naloxone, there was no significant difference between animals with and without seizure response in both sexes. The results suggest that in the preoptic opioid system there is no difference according to sex in the control of LH, and only a small one, if any, in the control of PRL. Further, on the basis of previous reports, there is a GABAergic system in the preoptic region, that is antagonized by naloxone and causes the activation of cortical neuronal activity.     

Possible dopaminergic system involvement in LH and PRL responses to naltrexone treatment

Naltrexone (Nalt) causes a rapid increase in luteinizing hormone (LH) level. This short term increase of LH concentration declines to baseline levels in less than 1 hour. Addition of pimozide (0.1 mg) caused a blunted response to Nalt challenge, with significantly reduced LH peak values compared with Nalt treatment alone. Pimozide alone caused a delayed decrease compared with baseline LH values. By following plasma prolactin (PRL) levels it was shown that pimozide administration increased PRL levels rapidly for more than 2 hours. Addition of Nalt to pimozide-treated rats significantly decreased plasma PRL values compared with pimozide alone. Nalt injected by itself attenuated PRL baseline levels. Thus, the mechanism by which pimozide caused PRL elevated level is via the dopaminergic as well as the opioid system. It is suggested that the opioid system controls plasma PRL and LH levels through other hypothalamic neurotransmitters in addition to dopamine.     

Synthesis of α-Adenosine 5′-Monophosphate

The distributions of protein, calcium and inorganic phosphate among casein micelles of skimmilk before and after frozen storage were investigated by gel filtration through Sephadex G-200 with 6.6 m urea solution as eluant.

The results showed that the native casein micelles were fractionated into two fractions. Fast eluting fraction contained large amount of calcium and inorganic phosphorus. Slow eluting fraction contained calcium but was essentially free of inorganic phosphorus. Frozen storage caused the increase of proportion of the fast eluting fraction accompanying the increase of calcium and inorganic phosphorus contents in it. It is suggested that the salt linkage newly formed during frozen storage causes the increase of proportion of the fast eluting fraction.     

Decrease in serum prolactin during bromocriptine-induced pregnancy and subsequent restoration of reproductive function in some hyperprolactinemic women

Twenty-two women with hyperprolactinemia and amenorrhea were followed up for at least 18 months after 22 bromocriptine-induced full term pregnancies. Return of menstruation occurred in 9 of the 22 patients after pregnancy. Five of them conceived subsequently without any treatment. The prolactin (PRL) concentration before or during bromocriptine treatment was not significantly different between the patients who conceived spontaneously and those who did not. However, the PRL concentration after weaning was significantly lower in the patients who conceived spontaneously than in those who did not. Serum PRL levels were normal or only slightly elevated in the patients who conceived spontaneously. In 11 of the 22 patients, PRL levels were serially determined during bromocriptine-induced pregnancies. In 7 of the 11 patients, serum PRL levels fell during the second or third trimester. Spontaneous pregnancy occurred in 3 of the 7 patients who showed a decrease in PRL values during pregnancy, but in none of the 4 patients who did not. Furthermore, PRL levels after weaning correlated with PRL levels during the third trimester in these 11 women. Consequently, a decrease in PRL values during pregnancy may result in a fall in PRL levels after pregnancy, which in turn leads to the restoration of reproductive function in some subjects.     

Prolactin and insulin are targeted to the regulated pathway in GH4C1 cells, but their storage is differentially regulated

PRL storage in GH4C1 cells, rat pituitary tumor cells, can be induced by treatment with a combination of estradiol, epidermal growth factor, and bovine insulin. This increase in storage is characterized by a preferential increase in intracellular PRL compared with secreted PRL and a 50-fold increase in the number of secretory granules. Treatment with the combined hormones stimulates PRL synthesis approximately 6-fold, but this effect is not sufficient to increase PRL storage, because epidermal growth factor alone increases PRL synthesis to the same extent without affecting storage. The cDNA for human proinsulin down-stream of the RSV-LTR promoter was transfected into GH4C1 cells to determine whether storage of another protein known to be targeted to the regulated pathway would also increase with hormone treatment. Proinsulin and PRL release were stimulated over the same time course and to the same peak height, compared to basal release, by both KCl and TRH, indicating that proinsulin is targeted to the regulated pathway in GH4C1 cells. There was little intracellular processing of proinsulin to insulin. Proinsulin synthesis increased 3.9-fold with the combined treatment, assessed by accumulation of proinsulin immunoreactivity in the medium and increases at the mRNA level. Treatment with the combined hormones did not cause the preferential increase in intracellular proinsulin that occurred with PRL; the increase in intracellular proinsulin could be accounted for primarily by effects on synthesis. These results suggest that storage of the two hormones can be differentially regulated.     

Twenty-Four-Hour Prolactin Profiles in Night Workers

In addition to sleep processes, it has been suggested that an intrinsic circadian rhythmicity is involved in the temporal organization of prolactin (PRL) secretion. Eight night workers were studied to determine whether the PRL rhythm is adapted to their rest-activity schedule and whether this provides evidence in favor of an endogenous clock-driven component. Ten day-active subjects, sleeping once during the night and once after an 8-h delay in their sleep period, were used as a control group. Plasma PRL, body temperature, and plasma melatonin were measured at 10-min intervals. Twenty-four-hour PRL profiles did not differ between night workers sleeping as usual during the daytime and day-active subjects submitted to an abrupt sleep shift to daytime. For the two groups of subjects a transient PRL peak, similar in size and time of occurrence, was observed during the night. Melatonin, a strong marker of the primary circadian oscillator, displayed a phase shift that differed widely among night workers. Body temperature, on the other hand, was found to be more regularly adapted despite the persistence of a small decrease or leveling off during the night. Although no relationship was found between the melatonin increase and the nocturnal PRL peak, a concomitance with this transient temperature decrease could be demonstrated. The persistence of this PRL peak in night workers raises the question of its significance. (Chronobiology International, 13(4), 283-293, 1996)     

Relative zinc-binding activities of ligands in the cytosol of rat small intestine

Relative zinc-binding activities of high-molecular-weight zinc-binding ligand (HMW-ZBL), metallothionein (MT) and low-molecular-weight zinc-binding ligand (LMW-ZBL) in the cytosols of rat small intestines under various experimental conditions were examined. Zinc-binding activities of MT decreased and those of LMW-ZBL increased in the intestinal cytosols from most of the experimental rat groups after incubating at 37 degrees C for 2 hr. The relative zinc-binding activity of MT increased with increasing doses of injected zinc and decreased with orally-administered zinc. Isolated MT did not lose zinc-binding activity during incubation at 37 degrees C for 48 hr, but moved from the MT eluting peak to the LMW-ZBL eluting peak after 1 week.