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G. J. Boer
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J. Kruisbrink
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ABSTRACT

A controlled-delivery module based on microporous Accurel polypropylene tubing, implanted subcutaneously in the rat, was used to release oxytocin for at least 40 days both in vitro and in vivo. Using a dosage rate of approximately 650 ng oxytocin per day and implanting the device in rats on day 17 of pregnancy, the known physiological action of oxytocin in advancing labour was confirmed. The increased concentrations of oxytocin in the mothers gave rise to adverse effects; the course of labour was protracted during expulsions of the first pups and the birth weight was reduced. Postnatally, body development of the pups was also affected, although there was partial recovery when the pups started to feed independently. Both pre- and postnatal exposure of pups to an oxytocin-treated mother reduced their body water turnover measured at 1 month of age.

The effects on the course of parturition and during lactation might be explained by a blockade of uterine and mammary gland oxytocin receptors respectively, thereby inhibiting a proper response to pulsatile endogenous oxytocin secretion. The changes in water metabolism, which are opposite to those described for the heterologous hormone vasopressin, are less easy to explain since maternal oxytocin is not supposed to pass the placenta. The results may indicate that clinical use of oxytocin for induction of labour and lactation may have hitherto unrecognized side-effects.

J. Endocr. (1984) 101, 121–129

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G. J. Boer
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M. Rieutort
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Levels of GH in serum were assayed during the development of heterozygous (HET) control and vasopressin-deficient homozygous (HOM) Brattleboro rats. In early postnatal growth no differences in GH concentrations were present between HET and HOM rats for the rapid decline in serum levels of GH in the first week and the constant period up to day 24 of age thereafter. However, higher values were found in 55-day-old HOM rats and lower values at the age of 9 months. It is concluded that the stunted development of the body and brain of HOM rats is not GH-related, and that changes or anomalies in GH secretion appear only after neurogenesis has been completed.

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J. Kruisbrink
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J. J. van Heerikhuize
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G. J. Boer
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ABSTRACT

The cerebrospinal fluid level of arginine vasopressin (AVP) or vasoactive intestinal polypeptide (VIP) was enhanced chronically by implantation of a device for controlled drug delivery in the lateral ventricle of the rat. Urine production, water consumption, urine osmolality as well as urinary AVP excretion were then measured for a period of 26 days. During this period the rats were studied under normal hydration and under conditions of osmotic stress induced by water deprivation (2 days) and the drinking of 2% (w/v) NaCl (6 days), in order to see whether the capacity of central systems to react adequately to osmotic stimuli was affected by high central peptide levels.

Immediately after the central AVP treatment was started, a temporary increase was found in urinary AVP levels which was not accompanied by a change in any of the other parameters but which decreased again to control levels within 10 days. After this burst of AVP excretion, AVP-treated rats showed a tendency during periods of normal hydration for a lower urine osmolality, combined with a higher water intake and urine production without changes in urinary AVP excretion. Since there was no clear-cut correlation between urinary AVP excretion and body water turnover, this could still indicate a slowly acquired and slight inhibition of pituitary AVP release by long-term centrally administered AVP. However, the capacity of these rats to respond to osmotic stimuli was not different from the controls.

In the VIP-treated rats a slight but significant reduction in urine production was found in all three periods of normal hydration. During the osmotic stress induced by the drinking of 2% NaCl the VIP-treated rats showed a lower increase in urine production and fluid intake and a lower decrease in urine osmolality when compared with the response of the control rats. This has tentatively been interpreted as a potentiation by VIP of the activation of pituitary AVP release under these conditions.

J. Endocr. (1988) 117, 207–214

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N. H. Herzberg
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E. Goudsmit
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J. Kruisbrink
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G. J. Boer
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ABSTRACT

Young, middle-aged and aged rats received s.c. testosterone implants for 50–52 days in order to investigate whether supplementation of testosterone in aged rats could normalize the reported reduction of kidney arginine vasopressin (AVP)-binding sites and increase the plasma concentration of AVP. Receptor number, which was measured by means of a membrane-binding assay with [3H]AVP as ligand, was below the detection level in the untreated aged rat. Following testosterone treatment, no effects were seen in the youngest groups, but in the aged group AVP receptors became clearly detectable, albeit with a lower affinity. A remarkable observation was the increase in affinity for renal AVP binding in the middle-aged compared with the young rat. Plasma levels of AVP in control aged rats tended to be higher. Such a tendency was completely absent in the testosterone-treated aged rats. Possible mechanisms underlying the restoration of reduced AVP-binding sites in the kidney of the aged rat by testosterone treatment are discussed.

Journal of Endocrinology (1989) 123, 59–63

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G. J. Boer
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J. Kruisbrink
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H. van Pelt-Heerschap
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A long-lasting and constant release of vasopressin in serum solution (in vitro) for periods up to 50 days can be obtained by the use of small-diameter microporous Accurel polypropylene tubing, filled with vasopressin and covered with collodion. The potency of the preparation is shown in vivo after subcutaneous implantation in the adult vasopressin-deficient Brattleboro rat, for which normal levels of urine production and osmolality were achieved at least for 1 month. The possible use of this method for other peptides and its application in small or immature laboratory animals and in fetuses is emphasized.

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H. D. Nicholson
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S. E. F. Guldenaar
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G. J. Boer
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B. T. Pickering
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ABSTRACT

The long-term effects of oxytocin administration on the testis were studied using intratesticular implants. Adult male rats had an Accurel device containing 20 μg oxytocin (releasing approximately 200 ng/day) implanted into the parenchyma of each testis; control animals received empty devices. The animals were killed at weekly intervals for 4 weeks. Some animals were perfused and the testes processed for light and electron microscopy. Blood was collected from the remaining animals for the measurement of testosterone, dihydrotestosterone, LH, FSH and oxytocin; epididymal sperm counts were measured and the testes were extracted and radioimmunoassayed for testosterone, dihydrotestosterone and oxytocin.

Long-term administration of oxytocin resulted in a significant reduction in testicular and plasma testosterone levels throughout the 4-week period examined and, after 14 days of treatment, lipid droplets were seen in the Leydig cells of treated but not control animals. Concentrations of dihydrotestosterone in the plasma and testes of the oxytocin-treated animals, however, were significantly elevated after 7 and 14 days and at no time fell below control values. Plasma FSH levels were also lower in the oxytocin-treated animals. Intratesticular oxytocin treatment did not affect LH or oxytocin concentrations in the plasma, epididymal sperm counts or the number of Leydig cells in the testis. Empty Accurel devices had no effect on testicular morphology.

This study provides the first evidence that oxytocin in vivo can modify steroidogenesis in the testis.

Journal of Endocrinology (1991) 130, 231–238

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Katja J Teerds Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
Human and Animal Physiology Group, Department of Animal Sciences, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands
Department of Internal Medicine, Erasmus Medical Centre, Erasmus University, Rotterdam, The Netherlands

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Eddy Rijntjes Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
Human and Animal Physiology Group, Department of Animal Sciences, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands
Department of Internal Medicine, Erasmus Medical Centre, Erasmus University, Rotterdam, The Netherlands

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Margarita B Veldhuizen-Tsoerkan Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
Human and Animal Physiology Group, Department of Animal Sciences, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands
Department of Internal Medicine, Erasmus Medical Centre, Erasmus University, Rotterdam, The Netherlands

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Focko F G Rommerts Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
Human and Animal Physiology Group, Department of Animal Sciences, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands
Department of Internal Medicine, Erasmus Medical Centre, Erasmus University, Rotterdam, The Netherlands

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Mieke de Boer-Brouwer Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
Human and Animal Physiology Group, Department of Animal Sciences, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands
Department of Internal Medicine, Erasmus Medical Centre, Erasmus University, Rotterdam, The Netherlands

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Luteinising hormone (LH) appears to be important for the establishment of the adult-type Leydig cell population. The role of LH in the initial steps of stem Leydig cell/precursor cell differentiation is less clear. The aim of the present study was to elucidate the role of LH in the differentiation of spindle-shaped mesenchymal-like cells into Leydig cell progenitors. Interstitial cells were isolated from rat testes at three different ages reflecting different phases in development, and cultured in the presence of increasing concentrations of LH (ranging from 0.01 to 10 ng/ml). Cells were isolated from 10-day-old rats when stem Leydig cells/precursor cells are abundant; 13-day-old rats when the first 3β-hydroxysteroid dehydrogenase (3β-HSD)-positive Leydig cell progenitors have developed in the strain of rats used in this study; and 18-day-old rats just prior to the wave of progenitor proliferation. Immunohistochemistry revealed that before stem Leydig cells differentiate into progenitor cells, they acquire functional LH receptors and become precursor cells. This was confirmed by an in vivo immunohistochemical double-labelling experiment. Addition of LH to the cultures increased the percentage of LH/3β-HSD-labelled Leydig cell progenitors, while the percentage of cells solely expressing the LH receptor decreased. Cell proliferation was negligible, suggesting that the increase in 3β-HSD-positive cells is the result of precursor cell differentiation. When interstitial cells were isolated from 13-day-old rats and to a lesser extent from 10-day-old rats, a small proportion of the precursors could develop into progenitor cells independent of the presence of LH. In conclusion: before Leydig stem cells differentiate into 3β-HSD-positive progenitor cells, they acquire LH receptors and become precursor cells. LH appears to be essential, even at very low doses for the differentiation of these precursor cells into 3β-HSD-positive progenitors, although a subpopulation of precursor cells can develop into progenitors independently of LH.

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J A M van der Post
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B J A van Buul
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A A M Hart
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J J van Heerikhuize
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G Pesman
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J J Legros
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E A P Steegers
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D F Swaab
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K Boer
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Neurohypophysial hormones are thought to be involved in alterations in fluid balance during pregnancy and delivery. In the course of normal pregnancy intravascular volume is increased whereas sodium restriction is thought to reduce plasma volume and cardiac output. In the present study, we measured the effect of long-term severe sodium restriction on vasopressin (AVP) and oxytocin (OT) levels during normal pregnancy and after delivery.

Fifty-nine healthy nulliparous women were randomized either for a low sodium diet (20 mmol sodium daily) or for a normal diet from week 12 of pregnancy onwards. Circulating plasma levels and urinary excretion of AVP and OT, their neurophysins (Np-AVP and Np-OT) and AVP bound to platelets were determined at regular intervals during pregnancy and after delivery. After completion of the study, women on a sodium-restricted diet were compared with control women on a normal diet using repeated measurement ANOVA with adjustment for potentially confounding variables.

After randomization, a reduction in urinary sodium excretion of, on average, 40–82% was found. In general, no effect of sodium restriction could be demonstrated on the various parameters (0·53<P<0·98) with the exception of a significantly lower 24-h urinary AVP excretion by non-smokers with sodium restriction compared with non-smokers having a normal diet (P=0·018) For all parameters, clear changes were found in the course of pregnancy and puerperium (P<0·0001 to P<0·005). Platelet-bound AVP decreased and Np-OT increased during pregnancy. After birth, free plasma AVP, plateletbound AVP, OT, osmolality, sodium and potassium increased, while Np-AVP and Np-OT decreased.

Although elevated Np-AVP and Np-OT levels during pregnancy seem to indicate increased release of neurohypophysial hormones, pregnancy up to 36 weeks of gestation is accompanied by low circulating AVP and OT levels.

Long-term severe sodium restriction diminishes urinary AVP excretion in (non-smoking) pregnant women, without changing circulating levels of AVP and OT, despite the known reduction in circulating volume. The reduced circulating (platelet-bound) AVP levels during pregnancy, whether or not in combination with severe sodium restriction, support the absence of significant non-osmotic stimulation of AVP during pregnancy.

Journal of Endocrinology (1997) 152, 345–354

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