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Biomedical subjects

A G Robinson

Publications and source records attributed to A G Robinson.

At least 37 records · Page 2Linked to original sources
PubMed1989

Endocrine function in patients with large pituitary tumors treated with operative decompression and radiation therapy.

Large pituitary tumors are still a common problem. Thirty consecutive patients underwent operative decompression and radiation therapy for large sellar and suprasellar tumors. They were studied prospectively in terms of their endocrine outcome. Ten of the patients had panhypopituitarism both before and after treatment. The other 20 patients had partial hormonal deficits prior to treatment. Ten (50%) of the 20 patients who had partial preoperative deficits went on to develop delayed onset of worsening in their endocrine function; 9 of the 10 developed panhypopituitarism, and 1 patient developed decreased thyroid function. The mean time from surgery until the onset of delayed worsening in endocrine function was 26.1 months. The mean age of those patients who developed delayed onset of worsening in pituitary function was significantly higher than that of those who did not develop further hormonal loss (40.5 +/- 3.1 years versus 52.0 +/- 4.1 years, P less than 0.05). None of the 10 patients with delayed onset of worsening in pituitary function had anatomical evidence by computed tomographic scan of tumor recurrence. Delayed onset radiation effect is the most likely cause of the late onset of worsening in endocrine function.

Combined Modality Therapy↗
PubMed1988

Effect of protein intake and urea on sodium excretion during inappropriate antidiuresis in rats.

Administration of urea to patients with the syndrome of inappropriate antidiuresis (SIAD) is thought to ameliorate hyponatremia by both producing an osmotic diuresis and diminishing ongoing natriuresis. The present study evaluated these effects in a rat model of SIAD utilizing dilutional hyponatremia induced by continuous infusion of 1-deamino-[8-D-arginine] vasopressin. Following 48 hours of sustained hyponatremia, separate groups of rats were then refed with either: (1) 5% dextrose alone, (2) a 20% protein chow, (3) an isocaloric protein deficient (0%) chow, or (4) the isocaloric protein-deficient chow supplemented with oral urea. Our results demonstrate that rats refed a 20% protein diet significantly improved their plasma [Na+] as compared to rats refed protein deficient diets, and this improvement was accompanied by decreases in natriuresis despite an increased glomerular filtration rate and an unchanged negative free water clearance. Identical effects were observed in rats refed a protein deficient diet but supplemented with oral urea, suggesting that urea generation from catabolism of dietary protein is responsible for the effect of protein refeeding to decrease urinary sodium excretion. Both the protein and urea refed rats had significantly higher inner medullary urea contents and concentrations compared to rats refed protein-deficient diets and also to rats studied immediately before protein refeeding, supporting the hypothesis that urea and dietary protein decrease natriuresis in patients with SIAD in association with increased inner medullary urea concentrations.

Animals↗
PubMed1988

Arginine vasotocin and a novel oxytocin-vasotocin-like material in plasma of human newborns.

Plasma of human adults contains an oxytocin, vasotocin-like (OT-VT) immunoreactive material that is estrogen responsive in both males and females and the levels of which are elevated during pregnancy. Although OT-VT is immunoreactive with an antiserum raised against synthetic arginine vasotocin (AVT), the elution profile of OT-VT by high-performance liquid chromatography (HPLC) is distinct from AVT, arginine vasopressin (AVP) or oxytocin (OT). Because the fetus is also exposed to high estrogen levels during pregnancy and AVT has been reported to be present in human fetal pituitaries, cord blood samples from 16 vaginally delivered human newborn infants were examined for evidence of OT-VT and AVT. Analysis of an extracted pool of cord blood plasma by HPLC revealed 4 peaks (I-IV) of AVT-like immunoreactivity. Peaks II and IV coeluted with synthetic AVP and OT, respectively, and were attributable to cross-reaction of the AVT antiserum with these peptides. Peak I was identified as AVT on the basis of its coelution with synthetic AVT. Peak III eluted in a manner identical with OT-VT. These results indicate that human newborn plasma contains at least three neurohypophysial peptides, AVP, OT and AVT. Additionally, newborn plasma contains an AVT-like immunoreactive material that is distinct from AVT, AVP and OT, but is identical with a novel OT-VT material observed in plasma of estrogen-primed adults. The physiological significance of AVT and OT-VT in newborn plasma remains to be determined.

Arginine Vasopressin↗
PubMed1988

Vasopressin stimulation of adrenocorticotropin hormone (ACTH) in humans. In vivo bioassay of corticotropin-releasing factor (CRF) which provides evidence for CRF mediation of the diurnal rhythm of ACTH.

The diurnal response of ACTH release to intravenously administered arginine vasopressin was tested in normal volunteers given consecutively moderate doses of vasopressin every 15 min (0.1, 0.3, 1.0, and 3.0 IU) at 2200 h and again at 0700 h (PM/AM). This protocol was repeated 4 wk later with the times reversed (AM/PM). A dose-related increase in ACTH secretion was observed in all subjects. When the AM response of the AM/PM protocol was compared with the PM response of the PM/AM protocol, the release of ACTH was greater in the morning (P less than 0.05) as evaluated by the following criteria: peak value of ACTH (129.9 +/- 30.4 pg/ml in the AM vs. 57.1 +/- 20.2 in the PM); area under the curve (689 in the AM vs. 259 in the PM); and, sensitivity of the ACTH dose-response curve (first significant increase in ACTH with 1 IU of vasopressin in the AM but not significant even after 3 IU in the PM). In addition, when the AM vasopressin testing followed a previous evening stimulation (PM/AM protocol), there was a blunted ACTH response compared with the AM/PM protocol. Corticotropin-releasing factor (CRF) is probably the major ACTH secretagogue, but since vasopressin acts synergistically with CRF to produce an augmented release of ACTH, we suggest that the ACTH response to administered vasopressin depends upon the ambient endogenous level of CRF. We interpret our data and published data that CRF produces a lesser release of ACTH in the AM as follows: in the morning endogenous CRF is high and administered CRF produces little further release of ACTH, but administered vasopressin acting synergistically with high endogenous CRF causes a greater release of ACTH; conversely, in the evening endogenous CRF is low and administered CRF causes a greater release of ACTH, but vasopressin (a weak secretagogue by itself) gives a low ACTH response. We conclude that vasopressin stimulation of ACTH secretion can be used as an in vivo bioassay of endogenous CRF, and that there is a diurnal rhythm of CRF in hypophyseal portal blood.

Adrenocorticotropic Hormone↗
PubMed1988

Stereotaxic intracavitary irradiation for cystic craniopharyngiomas.

Stereotaxic intracavitary irradiation with instillation of phosphorus-32 (32P) colloidal chromic phosphate was performed in nine patients with cystic craniopharyngiomas. Serial neurological, ophthalmological, neuroendocrinological, and radiological examinations were performed before and after treatment. Dosimetry was determined based on a computerized tomography (CT) estimation of tumor volume, and was calculated to provide a tumoricidal dose (200 to 300 Gy) to the cyst wall. The follow-up period ranged from 14 to 45 months (mean 27 months). After treatment, all nine patients showed improvement of symptoms and radiological evidence of cyst regression. Because of an expanding solid component producing recurrent symptoms, one patient required a craniotomy 14 months after isotope instillation. Three of five patients with impaired visual acuity before surgery had significant improvement in acuity after treatment. Preoperative visual field defects in eight patients improved in four after 32P therapy. Of seven patients with preoperative endocrine abnormalities, one individual showed almost complete normalization and another had improvement in endocrine function. Patients who exhibited residual neuroendocrine function before isotope instillation developed no significant deterioration in endocrine status during the follow-up period. The findings suggest that stereotaxic intracavitary irradiation is a safe and effective treatment which should be considered as the initial surgery for cystic craniopharyngiomas.

Adolescent↗
PubMed1987

Identification of a corticotropin-releasing factor-binding protein in the plasma membrane of AtT-20 mouse pituitary tumor cells and its regulation by dexamethasone.

CRF stimulates the synthesis and secretion of proopiomelanocortin-derived peptides from AtT-20 mouse pituitary tumor cells. This study has shown that there is a specific binding site for CRF located on the plasma membrane of these cells. Both [125I]iodo-Tyr0CRF and noniodinated CRF (10(-11)-10(-7) M) stimulated, in a dose-dependent manner, the secretion of equimolar amounts of beta-endorphin-like immunoactivity from AtT-20 cells. Disuccinimidyl suberate, a cross-linking agent, was used to demonstrate specific binding of [125I]iodo-Tyr0CRF to plasma membranes from these cells. After cross-linking [125I] iodo-Tyr0CRF, the membrane proteins were solubilized with sodium dodecyl sulfate and electrophoresed on a 10% polyacrylamide gel. A single radioactively labeled band, corresponding to a mol wt of 66,000, was identified by autoradiography. [125I]Iodo-Tyr0CRF binding to these membranes was inhibited by 10(-7) M unlabeled CRF or an equimolar concentration of the CRF analog sauvagine. Similar concentrations (10(-7) M) of TRH, GnRH, insulin, [Arg8]vasopressin, somatostatin, and ACTH did not inhibit [125I]iodo-Tyr0CRF binding to the plasma membranes. Incubation of AtT-20 cells for 24 h in the presence of 10 nM dexamethasone reduced [125I]iodo-Tyr0CRF binding by 80% compared to that in untreated cells. Dexamethasone also inhibited the CRF-stimulated beta-endorphin-like immunoactivity secretory response. These data indicate that binding of CRF to a specific membrane protein is an integral component in the stimulation of AtT-20 cells by CRF.

Animals↗
PubMed1987

Clearance studies of oxytocin in humans using radioimmunoassay measurements of the hormone in plasma and urine.

Synthetic oxytocin (OT) was infused iv in four men at 3 mU/min, and the rate was doubled every 90 min for a total of three infusion periods. The mean (+/- SEM) OT MCR was 16.4 +/- 1.7 ml/kg X min and was independent of the rate of infusion. A method for measuring OT in urine was developed using an octadecasilyl-silica column for extraction of the hormone. The extracted residue was reconstituted in potassium phosphate buffer, pH 7.4, for RIA. The minimum detectable level of OT in urine was 0.2 microU/ml (defined as a bound to free ratio of approximately 90%). The mean recovery of OT was 77 +/- 2%. The mean (+/- SEM) concentration of endogenous OT in urine was 10.2 +/- 1.4 microU/ml. Endogenous OT in urine eluted from a reverse phase high pressure liquid chromatography column as a single peak of OT immunoreactivity in the position of synthetic OT. Urinary OT excretion during infusion of synthetic OT was linearly correlated with plasma OT concentration whether calculated as microunits of urinary OT per mg creatinine (r = 0.89) or urinary OT per min (r = 0.93). Mean urinary fractional clearance of OT (OT clearance/creatinine clearance) was 3.6% renal clearance of OT (5.5 ml/min or 0.43% of MCR). Thus, OT MCR was constant over a wide range of physiological plasma OT levels and was similar to MCR in pregnant women studied previously in this laboratory. Less than 1% of OT was cleared in urine. This study defines the relationship between urinary and plasma OT during steady state infusion of physiological concentrations of the hormone and indicates that measurements of OT in urine by RIA may prove helpful for pharmacokinetic and physiological studies of OT-related events in humans.

Adult↗
PubMed1987

Cold water stimulation of oropharyngeal receptors in man inhibits release of vasopressin.

The act of drinking ameliorates thirst and inhibits the secretion of vasopressin before changes in extracellular fluid volume or osmolality in both animals and man. We evaluated whether this reflex inhibition of vasopressin secretion might be due to the presence of oropharyngeal receptors in humans. After dehydration, normal subjects (n = 4) were allowed to suck on ice chips for 30 min. Despite the absence of changes in plasma sodium (Na+) or osmolality, the mean plasma vasopressin level decreased promptly within 10 min from 2.8 to 1.8 pg/mL, and it remained low for 30 min after ice ingestion. When the dehydration protocol was repeated with the subjects receiving 100 mL water (25 C) for 30 min rather than ice chips, plasma vasopressin levels did not change. These data demonstrate that activation of cold-sensitive oropharyngeal receptors results in inhibition of vasopressin secretion independently of osmotic or gastric factors. In a second study 0.2 mL/kg X min 3% NaCl was administered for 90 min as a second stimulus to vasopressin secretion, and ice chips were given during the last 30 min of infusion. Plasma vasopressin levels increased steadily to 3.3 +/- 0.5 (+/- SEM) pg/mL by 45 min, and despite ice ingestion increased further to 4.6 +/- 0.8 pg/mL by 90 min. Consequently, hypertonicity appears to be a stronger stimulus to vasopressin release, since the suppressive effect of stimulation of oropharyngeal receptors with ice was not evident during the NaCl infusion. Finally, no changes in vasopressin levels were found in subjects holding concentrated NaCl solutions in their mouths for 30 min, indicating that the oropharyngeal receptors are not responsive to local changes in osmolality. The presence of such cold-sensitive oropharyngeal receptors may explain the desire of severely dehydrated patients, e.g. patients with diabetes insipidus, for cold liquids.

Adult↗
PubMed1987

Metastatic tumor of the pituitary gland.

Although metastatic tumors of the pituitary gland and the sellar region are not common, they may radiographically mimic a pituitary tumor. Because the metastasis frequently involves the posterior lobe and because lateral extension to the cavernous sinus is common, patients may present with ptosis, diplopia, or diabetes insipidus. Decrease in anterior pituitary function is less common. Metastatic tumors contain abundant vascular networks, as evidenced by frequent blush on cerebral angiography and increased bleeding at operation. We report the case of a 57-year-old woman who presented with rapid onset of bilateral ptosis and ophthalmoplegia and was found to have a metastatic carcinoma within the pituitary gland.

Brain Neoplasms↗
PubMed1987

The neurohypophysis: recent developments.

The hormones of the neurohypophysis, vasopressin and oxytocin, have now been shown to be synthesized as part of a prohormone complex that includes a vasopressin-neurophysin and oxytocin-neurophysin, respectively. In addition, for vasopressin, there is a glycopeptide as part of the prohormone. For each hormone the prohormone is packaged into neurosecretory granules and transported via axons to the posterior pituitary gland. In addition to this "classic" system, axons containing neurohypophyseal hormones project to the median eminence for release into portal vessels, and to other areas of the brain and spinal cord where the peptides may function as neurotransmitters rather than as hormones. As neurotransmitters, the neurohypophyseal hormones may be involved in the regulation of certain autonomic functions. Vasopressin and oxytocin are secreted into the cerebrospinal fluid where there is a diurnal rhythmic secretion of the peptides in several animal species (some species have a predominant rhythm of vasopressin and others a rhythm of oxytocin). Neurohypophyseal peptides are synthesized in some non-neuronal tissues where the function is unknown, and recently a novel peptide with similarities to oxytocin and vasotocin has been identified. The relationship of this novel peptide to the neurohypophyseal peptides is unknown. These new developments are likely to elucidate many new functions for the hormones of the neurohypophysis.

Adrenocorticotropic Hormone↗
PubMed1987

Increased levels of plasma renin, aldosterone, catecholamines and vasopressin in chronic ambulatory peritoneal dialysis (CAPD) patients.

Fluid excess can cause hyporeninemia and hypoaldosteronemia in hemodialysis patients. In six patients on CAPD, plasma renin activity (PRA) and plasma aldosterone (PA) were elevated to levels of : PRA 10.2 +/- 2.9 nl (1-5 ng/ml/h), and PA: 47.4 +/- 16.2 (normal 5-20 ng/dl). In 4 patients, data posthemodialysis and later during CAPD revealed that PRA increased from 0.9 +/- 0.3 to 14.1 +/- 4.6 and PA increased from 3.4 +/- 0.3 to 67.4 +/- 24.9 on CAPD (p less than 0.05). Mean arterial pressure was lower on CAPD and serum glucose was higher. No significant difference was seen in weight, hematocrit, BUN, or potassium, however. Plasma volume was not decreased in five CAPD patients: 3619 +/- 358 ml (predicted 3083 +/- 201 ml). Elevated catecholamine levels were seen in CAPD patients: norepinephrine 868.0 +/- 104.1 (normal 358.4 +/- 41.5 pg/ml), epinephrine 386.3 +/- 49.2 (normal 58.3 +/- 10.6 pg/ml). Plasma vasopressin levels were elevated to the range usually seen with hyperosmolality. In eight patients who lost or gained weight on CAPD, levels of PRA and PA changed as expected, but catecholamine levels did not correlate with weight changes. The data suggest that in CAPD patients, PRA and PA may be elevated in association with augmented sympathetic stimulation and elevated vasopressin levels. Serial observations demonstrated that PRA and PA can respond appropriately to changes in body weight, while catecholamine and vasopressin levels seem to be influenced by other factors.

Aldosterone↗
PubMed1987

High-performance liquid chromatographic characterization of neurophysins in chronic renal failure.

Levels of immunoreactive (IR) oxytocin (OT)-associated or estrogen-stimulated neurophysin (ESN) and vasopressin-associated or nicotine-stimulated neurophysin (NSN) were measured in plasma of patients with chronic renal failure before and after hemodialysis (HD) and intermittent peritoneal dialysis (IPD), and during continuous ambulatory peritoneal dialysis (CAPD). ESN-IR in 17 patients before HD was 24.4 +/- 2.7 ng/ml (mean +/- SEM) and increased after HD to 33.2 +/- 4.1 ng/ml (P less than 0.001). ESN-IR in 17 patients with CAPD was 15.2 +/- 3.4 ng/ml, significantly lower than in patients undergoing HD, P less than 0.001. In patients receiving IPD (n = 6), ESN was 11.6 +/- 3.7 ng/ml and did not change significantly after IPD. Levels of ESN in patients with renal failure were increased compared with levels in normal individuals, 1.0 +/- 0.1 ng/ml. Levels of ESN were not correlated with laboratory parameters that may be abnormal in renal failure. NSN levels in 16 of 17 patients undergoing HD were 3.2 +/- 0.34 ng/ml and in 14 of 17 patients with CAPD were 2.9 +/- 0.4 ng/ml, respectively. ESN before HD (r = 0.63, P less than 0.01), after HD (r = 0.85, P less than 0.001), and in patients with CAPD (r = 0.83, P less than 0.001) and IPD (r = 0.81, P less than 0.05) correlated significantly with an OT-like peptide previously found to be increased in renal failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

The plasma of pregnant women contains a novel oxytocin-vasotocin-like peptide.

Basal levels of immunoreactive oxytocin (OT) were measured in plasma of healthy pregnant women using two antisera to OT, Pitt Ab-1 and Pitt Ab-2, and an antiserum to arginine vasotocin, Tor AVT Ab. The mean (+/- SEM) level of immunoreactive OT Pitt Ab-1 was significantly higher, 7.7 +/- 0.9 microU/mL, than immunoreactive OT Pitt Ab-2, 0.9 +/- 0.2 microU/mL, P less than .001 measured in the same samples. AVT immunoreactivity in plasma of nonpregnant individuals was 0.8 +/- 0.16 pg/mL and in plasma of women in late pregnancy was 5.0 +/- 0.4 pg/mL. In four pregnant women receiving an infusion of synthetic OT (Pitocin, Parke-Davis, Morris Plains, NJ) a linear correlation was found between the dose of OT infused and the concentration of OT in plasma in samples measured with Pitt Ab-2, but no correlation was found in the same samples measured with Pitt Ab-1. Immunoreactive OT Pitt Ab-1 in plasma was not destroyed by a 60-minute incubation with pregnancy plasma. Pooled plasma from pregnant women was separated by reverse phase high pressure liquid chromatography (HPLC). OT Pitt Ab-1 and Tor AVT immunoreactivities in pregnancy plasma eluted in a position separate from synthetic OT. The differences found in levels of immunoreactive OT in the same samples of plasma measured with two antisera to OT illustrate an important reason why levels of OT in pregnant women may be reported to be variable among laboratories.

Chromatography, High Pressure Liquid↗
PubMed1986

Osmotic regulation of plasma vasopressin and oxytocin after sustained hyponatremia.

Endogenous pituitary secretion of vasopressin (AVP) and oxytocin (OT) was studied in rats with induced dilutional hyponatremia that was sustained for 2-5 days. Graded infusions of hypertonic saline produced progressive increases in plasma osmolality, but despite large relative increases in osmolality, AVP and OT secretion was not significantly stimulated until plasma [Na+] reached normal ranges. Regression analysis of plasma AVP and OT levels once secretion was stimulated showed no significant shift of the osmotic threshold for neurohypophyseal secretion of either hormone, as well as equivalent slopes of plasma AVP and OT increases per unit increases in plasma osmolality, in the hyponatremic rats relative to normonatremic controls. After a 20-25% decrease in plasma osmolality, total brain water content of hyponatremic rats increased only 3-6%, whereas larger decreases (11-17%) in total brain electrolytes were found. During subsequent hypertonic saline infusions in the hyponatremic rats total brain water content decreased linearly, resulting in brain dehydration below normal total brain water levels before stimulation of AVP and OT secretion occurred. The stability of the osmotic threshold for neurohypophyseal secretion, despite evidence of brain adaptation to chronic hypotonicity, argues that cell volume regulation via solute loss is not a likely cause of resetting of the osmostat. Additionally, brains of hyponatremic rats were found to manifest significantly greater susceptibility to dehydration after hypertonic saline infusions than brains of normonatremic controls, which may be a consequence of brain solute loss from adaptation to chronic hypotonicity.

Animals↗
PubMed1986

In vitro release of vasopressin and oxytocin from rat median eminence tissue.

Release of vasopressin (AVP) and oxytocin (OT) from rat median eminence and posterior pituitary tissue was studied in vitro by incubation in Krebs-56 mM KCl buffer. Both total tissue content and releasable pool of each hormone was measured in control rats, adrenalectomized rats and dexamethasone-treated rats. Adrenalectomy resulted in significantly increased release of AVP, but not OT, from median eminence tissue, whereas dexamethasone treatment failed to affect release of either hormone. Neither treatment had any effect on AVP or OT release from posterior pituitary tissue. Similarly, neither treatment caused any significant changes in total median eminence or posterior pituitary AVP and OT contents relative to controls, although dexamethasone-treated rats had a significantly lower posterior pituitary OT content than adrenalectomized rats. KCl-stimulated hormone release from median eminence tissue most likely represents an estimate of AVP and OT in zona externa terminals rather than in zona interna axons, because release was blocked by CoCl2 indicating calcium-dependent exocytosis. Immunohistochemical staining of median eminence tissue correlated well with the results of in vitro hormone release, in that increased AVP staining in the zona externa of adrenalectomized rats was also the only significant change noted using this methodology. Since increased levels of releasable AVP in the median eminence probably reflects similarly increased AVP levels in the hypothalamo-hypophyseal portal vessels of adrenalectomized rats, these results support a potential physiologic role for median eminence AVP, but not OT, in the chronic stimulation of adrenocorticotropin hormone secretion following adrenalectomy.

Adrenalectomy↗
PubMed1986

Ampholyte displacement and high pressure liquid chromatographic separation of the estrogen-responsive neurophysin from human plasma.

Estrogen-stimulated neurophysin (ESN) or oxytocin (OT)-neurophysin (Np) was measured in plasma of seven men before and after oral administration of 25 mg diethylstilbestrol (DES). Pre-DES levels of ESN averaged 0.93 +/- 0.3 (+/- SEM) ng/ml and increased to 29.8 +/- 6.5 and 25.4 +/- 5.1 ng/ml 24 and 48 h after DES treatment, respectively. To compare the estrogen-responsive Np in plasma with human OT-Np which is present in the posterior pituitary gland, the Np fraction of post-DES plasma was concentrated by double precipitation with ammonium sulfate and applied to ampholyte displacement and Sephadex G-75 columns. The Np fraction of this plasma extract contained ESN immunoreactivity (IR) but no nicotine-stimulated neurophysin-IR. ESN-IR of plasma and of an extract of human posterior pituitary eluted identically from a Sephadex G-75 column, indicating similar mol wt. The plasma extract containing ESN-IR eluted from the ampholyte displacement column at pH 4.3-4.2. No nicotine-stimulated Np (arginine vasopressin-Np)-IR was found in the plasma samples. ESN-IR in an extract of human posterior pituitary gland eluted from the ampholyte displacement column at the same pH as that of the ESN extracted from plasma. Peak ESN-IR-containing fractions from the ampholyte displacement were pooled, dialyzed, lyophilized, and reconstituted in appropriate carrier buffer for reverse phase high pressure liquid chromatography. The ESN-IR was resolved into two distinct ESN-IR peaks by high pressure liquid chromatography. Plasma and posterior pituitary gave identical pairs of peaks. Thus, the Np that is increased in human plasma in response to estrogen is identical to pituitary OT-Np, providing strong evidence that estrogen stimulates the human neurohypophysis.

Adult↗
PubMed1985

Antidiuretic effects of oxytocin in the Brattleboro rat.

The antidiuretic activity of oxytocin (OT) was measured in Brattleboro rats with congenital diabetes insipidus. A dose dependent antidiuretic response was found in animals receiving chronic infusions of 0.1 micrograms/h, 1.0 micrograms/h, and 5 micrograms/h of OT. OT infused at the rate of 5 micrograms/h over a 7-day period completely reversed the symptoms of diabetes insipidus. The results support the concept that OT serves as a weak agonist of vasopressin at the level of the kidney and at pharmacological levels exhibits antidiuretic activity.

Animals↗