Rat vasopressin response to insulin-induced hypoglycemia.

The effect of insulin-induced hypoglycemia upon plasma arginine vasopressin measured by a specific and sensitive RIA has been studied in unanesthetized male Sprague-Dawley rats. Hypoglycemia caused a 5-fold rise in plasma arginine vasopressin to a maximum of 28.0 +/- 9.1 pg/ml (mean +/- SD). This response was associated with a 2% fall in plasma osmolality, a rise in plasma sodium of less than 1%, a 10% fall in estimated blood volume, and no significant change in mean arterial blood pressure. PRA was increased 5-fold by hypoglycemia. However, beta-adrenergic blockade with propranolol completely prevented the renin response without altering the rise in vasopressin. In contrast, water loading abolished and hypertonic saline loading enhanced the effect of hypoglycemia on plasma vasopressin. We conclude that insulin-induced hypoglycemia stimulates vasopressin secretion by some as yet unrecognized primary mechanism whose responsiveness can be altered by changes in osmolality.

Vasopressin response to 2-deoxy-D-glucose in the rat.

The effect of 2-deoxyglucose (2DG) upon plasma arginine vasopressin (AVP), measured by a specific and sensitive RIA, has been studied in unanesthetized male Sprague-Dawley rats. Injection of the drug ip at a dose of 100 mg/kg BW caused a 10-fold rise in plasma AVP to 23.4 +/- 4.9 pg/ml (mean +/- SD). This effect was associated with a rise in plasmas osmolality to 301.8 +/- 3.9 mosmol/kg, but this change was accounted for totally by a rise in plasma glucose to 17.3 +/- 3.0 mM and in plasma urea to 3.4 +/- 0.4 mM. The only effective solute, plasma sodium, fell to 135.0 +/- 0.8 mM. Idiogenic osmoles did not change. Blood volume was reduced by about 5%, while PRA and mean arterial pressure did not change. Thus, the rise in plasma AVP caused by 2DG was not mediated by osmotic or hemodynamic stimuli. Treatment with propranolol (2.5 mg/kg BW) 15 min before 2DG completely abolished the AVP response. These results indicate that 2DG stimulates AVP release by a primary mechanism different from that which mediates the effect of insulin-induced hypoglycemia on AVP.

Arginine vasopressin and oxytocin responses to insulin-induced hypoglycemia in type 1 (insulin-dependent) diabetes.

In normal humans, arginine vasopressin and oxytocin are released acutely from the posterior pituitary gland in response to hypoglycemia, and their release may assist counterregulation. The responses of these hormones to insulin-induced hypoglycemia were measured in 16 insulin-dependent diabetic patients with no autonomic neuropathy (8 patients who had been diabetic less than 5 yr and 8 patients who had been diabetic greater than 15 yr) and in 6 normal subjects. The time of the onset of hypoglycemia and the mean blood glucose nadirs were similar in all groups, but the blood glucose recovery was delayed in the diabetic patients. In the normal subjects plasma arginine vasopressin rose from a mean basal value of 0.4 +/- 0.2 (+/- SE) pmol/L to a maximum of 1.3 +/- 0.6 pmol/L, and plasma oxytocin rose from 0.7 +/- 0.1 pmol/L to a maximum of 1.2 +/- 0.2 pmol/L 30 min after the onset of hypoglycemia. The plasma arginine vasopressin and oxytocin concentrations after hypoglycemia were significantly higher in both of the diabetic groups compared with those in the normal group. Arginine vasopressin and oxytocin rose in all control subjects after hypoglycemia. The individual hormonal profiles in the diabetic patients were variable, with an exaggerated rise of oxytocin in some diabetic patients and no rise in others. The arginine vasopressin responses were exaggerated in all of the diabetic patients. There was no correlation between the hormonal responses and the duration of diabetes. The exaggerated plasma arginine vasopressin and oxytocin responses to hypoglycemia in diabetic patients may indicate the failure of a normal inhibitory mechanism which modulates hormonal secretion or a compensatory response to impaired glucose recovery.

Arginine vasopressin response to insulin-induced hypoglycemia in man.

Insulin-induced hypoglycemia causes an increase in plasma vasopressin concentration in man and rat. To assess the mechanism by which this occurs, the effect of hypoglycemia was studied in healthy adults. After insulin injection, a 7-fold rise in plasma immunoreactive arginine vasopressin to 8.2 +/- 3.6 pg/ml was observed in 10 normal subjects. This was associated with a rise in plasma sodium of 2 meq/liter, but no significant change in mean arterial pressure or hematocrit was observed. The significance of the plasma sodium rise was assessed by observing the vasopressin response to hypoglycemia in a patient shown previously to have a selective loss of the vasopressin response to osmotic stimulation. His plasma vasopressin rose from 1.6 to 12.5 pg/ml with no fall in blood pressure or volume. beta-Adrenergic blockade with propranolol before repeat insulin-induced hypoglycemia did not reduce the vasopressin response (peak plasma vasopressin, 8.1 +/- 1.7 pg/ml), despite suppression of PRA. Linear regression analysis showed that the rise in plasma vasopressin and the percentage decline in plasma glucose correlated significantly (r = 0.57, P less than 0.001). In conclusion, hypoglycemia releases vasopressin nonosmotically by a mechanism that appears to be independent of factors currently known to effect vasopressin secretion.

Metastatic prolactinoma: effect of octreotide, cabergoline, carboplatin and etoposide; immunocytochemical analysis of proto-oncogene expression.

A 49-yr-old woman presented with an extensive prolactinoma (serum PRL > 10,000 mU/L, normal range < 450 mU/L). Over a 5-yr period following transsphenoidal surgery and pituitary irradiation, she became increasingly resistant to high doses of bromocriptine and underwent transfrontal surgery followed by stereotactic radiotherapy. In spite of these treatments, serum prolactin estimations rose progressively to > 100,000 mU/L. Magnetic resonance imaging scanning demonstrated a massive cystic tumor invading the temporal lobes, extending into the cervical and thoracic spine, with metastases to cervical lymph nodes. High-dose cabergoline administration resulted in a 30% decrease in serum PRL. Octreotide was administered as a continuous sc infusion with a profound analgesic effect on facial pain but with no effect on tumor progression. She was treated with a course of chemotherapy consisting of carboplatin and etoposide without any noticeable effect. The patient died 6 months following chemotherapy. Immunocytochemical analysis demonstrated positive nuclear staining for WAF-1, Rb protein, c-myc, and p53 both in the original and metastatic tumors. The metastases but not the primary tumor stained for c-jun. Metastatic prolactinoma remains a therapeutic challenge. It is associated with a variable proto-oncogene expression, which may be coincidental or causal. Cabergoline had no advantage over bromocriptine. Octreotide relieved facial pain but did not alter tumor progression. An effective therapy for metastatic prolactinoma remains to be identified.

Association analysis of the cytotoxic T lymphocyte antigen-4 (CTLA-4) and autoimmune regulator-1 (AIRE-1) genes in sporadic autoimmune Addison's disease.

Although autoimmune Addison's disease (AAD) may occur as a component of the monogenic autoimmune polyendocrinopathy type 1 syndrome (APS1), it is most commonly found as an isolated disorder or associated with the autoimmune polyendocrinopathy type 2 syndrome (APS2). It is likely that sporadic (non-APS1) AAD is inherited as a complex trait; however, apart from the major histocompatibility complex, the susceptibility genes remain unknown. We have examined polymorphisms at two non-major histocompatibility complex candidate susceptibility loci in sporadic (non-APS1) AAD: the cytotoxic T lymphocyte antigen-4 (CTLA-4) gene and the autoimmune regulator (AIRE-1) gene. DNA samples from AAD subjects (n = 90) and local controls (n = 144 for CTLA-4; n = 576 for AIRE-1) were analyzed for the CTLA-4A/G polymorphism in exon 1 of the CTLA-4 gene and for the common mutant AIRE-1 allele (964de113) in United Kingdom subjects with APS1, by using the restriction enzymes Bst7II and BsrBI, respectively. There was an association of the G allele at CTLA-4A/G in AAD subjects (P = 0.008 vs. controls), which was stronger in subjects with AAD as a component of APS2 than in subjects with isolated AAD. In contrast, the mutant AIRE-1 964del13 allele was carried in one each of the 576 (0.2%) control subjects and the 90 (1.1%) AAD subjects as a heterozygote (P = 0.254, not significant), suggesting that this common AIRE-1 gene abnormality does not have a major role in sporadic (non-APS1) AAD.

Prolactin stimulates Na+-K+-ATPase activity located in the outer renal medulla of the rat.

The effect of rat prolactin on rat renal Na+-K+-ATPase activity was investigated by a cytochemical technique. Rat prolactin caused stimulation of Na+-K+-ATPase activity only in the outer medulla of the kidney, and not in renal cortical structures. Peak enzyme activity in cultured rat renal segments occurred after tissue had been exposed to rat prolactin for 2 min, and the time of maximal stimulation did not vary with the concentration of prolactin. There was a curvilinear response in Na+-K+-ATPase activity over the rat prolactin concentration range, 0.04-40 ng/l, but higher prolactin concentrations caused inhibition of enzyme activity. Na+-K+-ATPase response was totally blocked by specific rat prolactin antiserum. Human prolactin had no consistent effect on rat medullary Na+-K+-ATPase activity. Addition of specific tri-iodothyronine and arginine vasopressin antisera to rat prolactin was without effect, confirming that the stimulatory action of rat prolactin on Na+-K+-ATPase was not due to contamination with these hormones which are known to stimulate this enzyme.

Stimulation of rat renal medullary Na+/K(+)-ATPase by arginine vasopressin is mediated by the V2 receptor.

In previous studies, we have demonstrated that 1-10 fmol arginine vasopressin (AVP)/l maximally stimulates the activity of the enzyme Na+/K(+)-ATPase in the rat renal medullary thick ascending limb (MTAL) of Henle's loop after 4 or 10 min of stimulation when measured using a cytochemical bioassay. We have tested the hypothesis that this stimulation is mediated by the V2 receptor in the MTAL. A cytochemical bioassay was used to investigate the effect of specific V1 and V2/V1 antagonists and a synthetic V2 agonist [1-deamino,8-D-arginine]-vasopressin (dDAVP), on the activity of Na+/K(+)-ATPase. There was no effect of the V1 antagonist (1 fmol-1 mumol/l) in inhibiting the activity of Na+/K(+)-ATPase stimulated by 1 fmol AVP/l. In contrast, 100 pmol of the V2/V1 antagonist/l significantly (P less than 0.001) inhibited the stimulation of Na+/K(+)-ATPase activity by 1 fmol AVP/l from 55.5 +/- 4.3 (S.E.M.) to 31.9 +/- 1.6 mean integrated extinction (MIE) after 4 min of stimulation and from 67.0 +/- 3.2 to 36.9 +/- 0.7 MIE after 10 min of stimulation. Similarly, the stimulation of Na+/K(+)-ATPase by 10 fmol dDAVP/l was inhibited by the V2/V1 antagonist from 55.1 +/- 1.0 to 26.1 +/- 0.5 MIE after 4 min of stimulation. We conclude that the stimulation of Na+/K(+)-ATPase by AVP is mediated by the V2 receptor in the rat renal MTAL.

Stimulation of Na+/K(+)-ATPase activity by polyamines in the rat renal medullary cells of the thick ascending limb of Henle's loop.

Previous studies have indicated that ornithine decarboxylase (ODC) may be involved in the stimulation of Na+/K(+)-ATPase activity by arginine vasopressin (AVP) in the rat renal medullary thick ascending limb of Henle's loop. The present study was aimed at establishing the role of the polyamines, the conversion products of ODC activity, in the stimulation of Na+/K(+)-ATPase by AVP. Using cytochemical methods, we have demonstrated an increase in Na+/K(+)-ATPase activity after stimulation with putrescine, spermidine and spermine (each 1 mmol/l) for 2.5, 2 and 1.5 min respectively. The specific inhibitors of spermidine and spermine synthase, bis-cyclohexylammonium sulphate and N-alkylated-1,3-diaminopropane respectively, inhibited the stimulation of Na+/K(+)-ATPase by AVP, this inhibition being reversed by spermine. These findings suggest that polyamines are involved in the stimulus-response coupling of the hormone-mediated response.

Stimulation of ornithine decarboxylase activity by arginine vasopressin in the rat medullary thick ascending limb of Henle's loop.

The effect of arginine vasopressin (AVP) on rat renal ornithine decarboxylase (ODC) activity was investigated by a cytochemical technique optimized for use in the medullary thick ascending limb of Henle's loop (mTAL). Stimulation of ODC activity by AVP was confined to the mTAL. Peaks in enzyme activity in cultured rat renal segments occurred after tissue had been exposed to AVP for 3 or 8 min and these times of maximal stimulation did not change with the concentration of AVP. There was a dose-dependent response in ODC activity over the AVP concentration range 0.01 10 fmol/l. The ODC response to AVP was totally blocked by specific antiserum to AVP and reduced by 70% with the specific inhibitor to ODC, difluoromethyl ornithine.

Inhibition of arginine vasopressin-stimulated Na+ K+ ATPase activity by difluoromethyl ornithine in the rat renal medulla.

Arginine vasopressin (AVP) stimulates Na+ K+ ATPase and ornithine decarboxylase (ODC) activity in the rat medullary thick ascending limb. The effect of difluoromethyl ornithine (DFMO), a specific inhibitor of ODC activity, on AVP-stimulated Na+ K+ ATPase activity was evaluated using a cytochemical bioassay. Peaks in Na+ K+ ATPase activity in cultured rat renal segments which occurred after tissue had been exposed to 1 fmol AVP/l were completely inhibited by the addition of 20 mmol DFMO/l to the culture medium containing AVP. The addition of 20 mmol DFMO/l to the culture medium containing AVP in the concentration range 0.001-10 fmol/l inhibited completely the stimulation of Na+ K+ ATPase activity by AVP. The response of Na+ K+ ATPase to increasing doses of ATP (10-40 g polypeptide/l) was not influenced by the addition of 20 mmol DFMO/l to the culture medium containing AVP, suggesting that the prevention of AVP-stimulated Na+ K+ ATPase activity by DFMO was not due to a direct effect on the enzyme.

Interference in the cytochemical assay of plasma vasopressin by a circulating factor induced by salt-loading in man.

Infusion of hypertonic saline into six normal volunteers caused an increase in plasma osmolality from 286.8 +/- 1.7 (mean +/- S.E.M.) to 307.6 +/- 2.6 mosmol/kg (P less than 0.001), a 7.1% increase in estimated blood volume, a rise in plasma immunoreactive arginine vasopressin (AVP) concentrations from 1.3 +/- 0.2 to 12.7 +/- 3.6 pmol/l (P less than 0.001) but no change in plasma AVP concentrations (2.1 +/- 0.9 and 1.9 +/- 1.3 pmol/l) as measured by a cytochemical technique based on the ability of AVP to stimulate rat renal medullary Na+/K+-ATPase activity. Addition of synthetic AVP to plasma obtained before, during and after hypertonic saline infusion also failed to stimulate Na+/K+-ATPase activity. The results suggest that infusion of hypertonic saline interfered with the cytochemical assay for AVP by inhibiting AVP-stimulated medullary Na+/K+-ATPase activity. We conclude that the use of this cytochemical method to detect plasma AVP has severe limitations under these experimental conditions.

Possible mechanisms responsible for the rise in plasma vasopressin associated with diabetic ketoacidosis in the rat.

The plasma concentration of arginine vasopressin (AVP) is increased in diabetic ketoacidosis (DKA) in man and the rat. Although haemodynamic changes and nausea/emesis may account for the increased secretion of AVP in severe human DKA, they appear not to be responsible in moderate DKA. Streptozotocin-treated rats were studied to investigate other factors possibly involved in the secretion of AVP in DKA. Wistar rats were injected i.p. with streptozotocin (150 mg/kg body weight). Diabetic rats were maintained on 3-4 units protamine-zinc insulin (PZI)/day for 11 days, after which PZI was withdrawn for 3 days in half the rats. The plasma concentration of AVP was greater in rats with DKA than in normal controls (mean 11.4 pmol/l compared with 1.6 pmol/l; P less than 0.05). Rats with DKA had higher plasma osmolality and concentrations of blood glucose, beta-hydroxybutyrate and acetoacetate, but lower plasma carbon dioxide content than diabetic and normal controls (P less than 0.05). There were no differences in plasma levels of sodium, urea or haematocrit between rats with DKA and controls. In a separate study involving the same procedures, daily systolic blood pressure was measured using a tail cuff to occlude arterial inflow to the tail, and subsequent detection of the cuff pressure at which the first arterial pulsation appeared. No significant differences were detected between normal and diabetic rats and rats with DKA. Exponential relationships between plasma osmolality and plasma AVP (correlation coefficient, r = + 0.75; P less than 0.01), and plasma ketone bodies and plasma AVP (r = +0.60; P less than 0.05) were obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Osmoregulation of vasopressin secretion in the insulin-withdrawn streptozotocin-treated diabetic rat.

To investigate whether hyperglycaemic ketoacidotic diabetic rats continue to osmoregulate the secretion of arginine vasopressin (AVP), male Wistar rats were injected with streptozotocin (150 mg/kg body weight). Rats rendered diabetic were maintained on protamine-zinc insulin (PZI) for 11 days (insulin-treated rats; n = 35), after which PZI was withdrawn for 72 h in half the rats (insulin-withdrawn rats). Insulin-withdrawn and -treated rats were divided into two groups; one was injected i.p. with distilled water (20 ml/kg) and the other with hypertonic saline (500 mmol NaCl/l; 20 ml/kg), and killed 30 min after injection. Insulin-withdrawn rats (water loaded and osmotically stimulated) were hyperglycaemic (16.5 +/- 0.8 and 16.5 +/- 0.9 mmol glucose/l respectively) and ketotic (2077 +/- 664 and 1474 +/- 170 mumol acetoacetate/l respectively). Insulin-treated rats were euglycaemic and non-ketotic. Osmotic manipulation caused similar changes in plasma sodium in both insulin-withdrawn and -treated rats. Plasma AVP was low in the water-loaded rats (0.6 +/- 0.1 and 4.5 +/- 0.9 pmol/l in the insulin-treated and -withdrawn rats respectively) and increased in rats injected with hypertonic saline (1.2 +/- 1.8 and 35.2 +/- 17.9 pmol/l respectively). There was no evidence of hypotension and hypovolaemia in any group of rats. Linear regression analysis defined the functions: plasma AVP = 2.56 (plasma Na-141), r = +0.63, P less than 0.01 for hyperglycaemic ketotic rats; plasma AVP = 0.83 (plasma Na-146), r = +0.78, P less than 0.001 for insulin-treated animals. The slopes and abscissal intercepts were significantly (P less than 0.05) different.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of acute pharmacological manipulation of central serotonin neurotransmission on osmoregulated secretion of arginine vasopressin in the rat.

To explore the hypothesis that serotonin (5-HT) is important in osmoregulated arginine vasopressin (AVP) secretion, we administered (i.p.) fluoxetine (FL) a 5-HT reuptake inhibitor (10 mg/kg body weight), ritanserin (RIT), an antagonist at the 5-HT2 and 5-HT1c receptor subtypes (1 mg/kg body weight), 1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride (DOI), a 5-HT2 receptor agonist (1 mg/kg body weight) or vehicle to rats 30 min before they were given an osmotic challenge. Rats received distilled water, normotonic saline (150 mmol NaCl/l) or hypertonic saline (500 mmol NaCl/l) (20 mg/kg i.p.) and were killed 30 min later. The osmotic stimulus alone produced significant (P < 0.001) effects on plasma osmolality and plasma sodium but FL, RIT and DOI did not have any significant effect on this stimulus. FL had no significant effect on the osmotic threshold of AVP release but significantly (P < 0.001) increased basal AVP secretion from 1.6 +/- 1.0 to 3.1 +/- 1.3 (S.E.M.) pmol AVP/l and significantly (P < 0.001) increased the AVP response to changes in plasma osmolality: vehicle-treated, 0.7 +/- 0.4; FL-treated, 1.7 +/- 0.2 pmol AVP/l per mOsm per kg. Neither RIT nor DOI had any significant effect on basal or stimulated AVP secretion. In a second study, RIT was administered 60 min i.p. prior to FL i.p. (doses as above), which was followed 30 min later by a hypertonic stimulus i.p. and rats were killed 30 min after hypertonic saline treatment. RIT had no significant effect on the AVP response to plasma osmolality and did not significantly alter the FL-augmented AVP response, suggesting that neither the 5-HT2 nor the 5-HT1c receptors are involved in the response of AVP to FL. We conclude that FL modulates osmoregulated AVP secretion but that the mechanism of this is unknown and is apparently not through the 5-HT2 or 5-HT1c receptor subtypes.

Altered osmotic thresholds for arginine vasopressin secretion and thirst during superovulation and in the ovarian hyperstimulation syndrome (OHSS): relevance to the pathophysiology of OHSS.

OBJECTIVE: To test the hypothesis that decreases in and maintenance of a new steady state in plasma osmolality and sodium level in ovarian hyperstimulation syndrome (OHSS) are due to altered osmoregulation of arginine vasopressin secretion and thirst. DESIGN: Prospective study. SETTING: IVF-ET program in a university-based assisted reproductive treatment center. PATIENT(S): Eight women undergoing superovulation for IVF-ET and five women with normal menstrual cycles. INTERVENTION(S): Two-hour infusion of 5% saline on day 3 or 4 after hCG administration in patients undergoing IVF or in the early luteal phase in controls. A 5% saline infusion test was done on day 10 after hCG administration in one patient with OHSS and one patient without OHSS, both of whom were undergoing IVF. MAIN OUTCOME MEASURE(S): Comparison of changes in thresholds for thirst and plasma vasopressin to plasma osmolality. Changes in urine osmolality, plasma electrolytes, hemoglobin level, and hematocrit were assessed at baseline and during infusion of 5% saline. RESULT(S): The sensitivity of the changes in arginine vasopressin secretion and thirst after 5% saline infusion was similar in IVF patients on day 3 or 4 after hCG and controls. However, the osmotic threshold was significantly lower by 6 mOsm/kg in IVF patients. By day 10 after hCG, the lower osmotic thresholds for arginine vasopressin secretion and thirst persisted in OHSS, although the sensitivity to arginine vasopressin secretion was markedly reduced. CONCLUSION(S): The osmotic thresholds for arginine vasopressin secretion and thirst are reset to lower plasma osmolality during superovulation for IVF-ET. This new lower body tonicity is maintained until at least day 10 after hCG in OHSS. Decreases in plasma osmolality and plasma sodium levels in OHSS are due to altered osmoregulation rather than electrolyte losses; correction of apparent "electrolyte imbalance" in OHSS is therefore inappropriate.

Immunoreactive vasopressin in end stage renal failure.

Patients with end stage renal failure have been shown to have higher basal concentrations of plasma arginine vasopressin than subjects with normal renal function. Immunoreactive vasopressin was detected in plasma from patients with severe chronic renal failure and a healthy subject at an elution volume identical to that previously determined with synthetic vasopressin. Assay of all fractions yielded identical chromatograms in the renal failure and healthy control groups. We conclude that the plasma immunoreactive vasopressin in end stage renal failure plasma coelutes with synthetic vasopressin and that the elevated concentrations found in these patients are not due to non-specific depression of binding in the vasopressin radioimmunoassay by circulating substances in renal failure.

Central-peripheral temperature difference, blood pressure, and arginine vasopressin in preterm neonates undergoing volume expansion.

AIM: To examine the effect of intravascular volume expansion for the treatment of hypovolaemia in sick preterm neonates. METHODS: An intravenous infusion of 20 ml per kg of 4.5% albumin was given to 14 preterm neonates. The effects on systolic blood pressure, central peripheral temperature difference (c-pT), and plasma arginine vasopressin concentration (pAVP) were measured. RESULTS: Thirteen babies showed a rise in systolic blood pressure. The six babies with the highest initial values of pAVP and c-pT showed a fall in both of these after infusion. The babies with lower initial pAVP (below 4 pmol/l) showed either a rise (two) or no change (six) after albumin infusion. There was a significant correlation between c-pT and log pAVP before (r2 = 0.61; p < 0.05) and after infusion (r2 = 0.45; p < 0.05). CONCLUSIONS: Plasma AVP concentration is related to c-pT in unwell preterm newborns. This study suggests that clinical assessment of hypovolaemia in preterm newborns is poor and could be improved by using c-pT.

Does positive pressure ventilation increase arginine vasopressin in preterm neonates?

AIM: To examine the effect of intermittent positive pressure ventilation (IPPV) on plasma arginine vasopressin concentration (pAVP) in preterm neonates. METHODS: Thirty five neonates were classified, at the time of blood sampling, into three groups: unstable ventilated; stable ventilated; and stable non-ventilated. A modification of an extraction method for pAVP was developed for use in studies on very small babies, and sampling methods were compared. RESULTS: The pAVP (median, range) was similar in the ventilated (1.85 pmol/l, 0.5 to 3.4) and non-ventilated (2.0, 0.5 to 2.6) stable babies, but was significantly higher (5.7, 1.1 to 25) in the unstable group. There was an inverse correlation between systolic blood pressure and pAVP concentration. CONCLUSIONS: This study shows that in preterm neonates pAVP concentration is affected by the clinical condition and blood pressure, but not by treatment with IPPV.

A new method for measuring the blood volume of the rat using 113mIndium as a tracer.

A new method is described for the estimation of blood volume in the rat using 113mIndium chloride. No in vitro labelling step is necessary as the isotope binds specifically to transferrin in vivo. Under anaesthesia, an external jugular vein was cannulated for blood sampling and indium chloride injected directly into a lateral tail vein. Three blood samples of 0.2 ml were taken at short intervals and radioactivity measured under standard conditions. Blood volume was found to be 7.46 +/- 0.14 (mean +/- SEM) ml/100 g body weight. Repeating the study of 5 animals gave similar values for blood volume on the 2 occasions (7.23 +/- 0.26 and 6.95 +/- 0.23 ml/100 g, P > 0.05). The new technique was compared with established methods using 51Cr labelled red blood cells and 125Iodinated albumin. In each animal, the 113mIndium technique produced values approximately 10% higher than those obtained using the sum of plasma and red cell mass, in keeping with the known difference between whole body and large vein haematocrit (Indium, 7.20 +/- 0.19 and Iodine with Chromium, 6.40 +/- 0.34 ml/100 g). Data on blood volume determined using 125Iodine as the tracer on these same animals were identical (Indium, 7.20 +/- 0.19 and iodine, 7.16 +/- 0.34 ml/100 g). The method is simple to perform and appears to be at least as accurate and reproducible as established methods for measuring blood volume.