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Biomedical subjects

D C Merrill

Publications and source records attributed to D C Merrill.

At least 55 records · Page 3Linked to original sources
PubMed1988

Role of vasopressin in regulation of sodium excretion.

It has been proposed that arginine vasopressin (AVP) contributes to the regulation of renal sodium excretion by direct intrarenal actions, by neural-hormonal interactions, and via secondary effects of fluid volume retention. The present studies were designed to determine the extent to which the natriuretic effects of AVP are secondary to volume expansion. Three groups of dogs were studied: the first was infused with AVP for 2 weeks in amounts that increased plasma levels from 3 to 15 pg/mL, while water intake was maintained constant by intravenous (iv) water infusion. The second group received the same amount of AVP and was permitted to drink ad libitum. The third group was infused with the same amount of AVP, while total body weight and volume were maintained at a constant level by use of an electronically servo-controlled water infusion system. The results showed a large increase in total body weight (+1.5 kg) and arterial pressure (mean arterial pressure (MAP); +40 mm Hg) in dogs receiving a fixed water intake. This was accompanied by a continuing natriuresis over a 2-week period and severe hyponatremia (115 mEq/L). Dogs allowed ad libitum drinking retained much less fluid (+0.5 kg). MAP was not significantly elevated, and natriuresis did not occur in this group, but hyponatremia was observed (130 mEq/L), and plasma renin activity (PRA) was suppressed. Servo-controlled dogs exhibited no change in MAP, plasma sodium, or PRA, and only a small (-15 mEq) natriuresis occurred on day 1 of AVP infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Control of adrenocorticotropin secretion and adrenocortical sensitivity in neurohypophysectomized conscious dogs: effects of acute and chronic vasopressin replacement.

We examined the effect of neurohypophysectomy with and without vasopressin replacement on the ACTH response to hypotension and ovine CRF infusion and on the adrenocortical response to ACTH and angiotensin II infusion in conscious dogs. Nitroprusside hypotension (decrease in mean arterial pressure of 25 mm Hg) in the intact state resulted in large increases in plasma arginine vasopressin (pAVP; from 2.6 +/- 0.3 to 296 +/- 63 pg/ml) and ACTH (from 35 +/- 6 to 395 +/- 92 pg/ml). Neurohypophysectomy resulted in greatly attenuated pAVP (8.4 +/- 1.6 pg/ml) and ACTH (80 +/- 10 pg/ml) responses to hypotension which were not normalized by physiological low dose vasopressin replacement (6-18 pg/kg.min continuously, iv, for 2 weeks). However, acute administration of vasopressin (4-6 ng/kg.min) simultaneously with hypotension in the neurohypophysectomized (neurohypox) dog, which produced pAVP levels equivalent to the hypotensive response to intact dogs, almost completely normalized the ACTH response to hypotension (to 248 +/- 74 pg/ml). The ACTH response to 20 ng/kg.min ovine CRF, iv (from 43 +/- 8 to 268 +/- 77 pg/ml), was not attenuated by neurohypophysectomy. The cortisol responses to infusion of 0.5 and 2 ng/kg.min ACTH-(1-24), iv, were essentially normal in neurohypox dogs. However, the ACTH and aldosterone responses to 5 ng/kg.min angiotensin II infusion iv were attenuated in neurohypox dogs off AVP replacement. Histological examination revealed normal adrenal glands and anterior pituitaries in neurohypox dogs. Immunocytochemical staining for vasopressin and neurophysin revealed normal cell bodies in the paraventricular and supraoptic nuclei of the hypothalami from neurohypox dogs. However, median eminence staining for AVP and neurophysin was greatly diminished in neurohypox dogs. In summary, neurohypophysectomy 1) attenuated the ACTH response to hypotension and angiotensin II, but not to CRF, and 2) attenuated the aldosterone response to high dose angiotensin II. Furthermore, the deficit in ACTH secretion was almost completely normalized by increasing plasma AVP levels to those observed in the intact dogs. We conclude that an action of circulating pAVP increases ACTH secretion by a direct effect at the pituitary and by activating afferent input to the hypothalamus.

Adrenal Cortex↗
PubMed1987

Electroanalgesia in urologic surgery.

Transcutaneous electrical nerve stimulation (TENS) was employed to reduce postoperative pain in 40 patients who had either radical nephrectomy, radical prostatectomy, or implantation of an inflatable penile prosthesis. These patients used 68 per cent less pain medication and made 84 per cent fewer requests for meperidine hydrochloride (Demerol) injections than did 40 control patients who had similar surgical procedures. The TENS units were easy to use, and there were no complications to electroanalgesia. The TENS program also was costeffective. TENS provided a simple, safe method of reducing postoperative pain in the three surgical procedures tested. Electroanalgesia may have application in other types of urologic surgery, and TENS should be particularly useful in patients who have outpatient surgery.

Analgesics↗
PubMed1987

Angiotensin II sensitization of aldosterone responsiveness to plasma sodium in conscious dogs.

Studies were performed to quantify the interaction of angiotensin II (ANG II) and plasma sodium (Na+) on the adrenal gland's ability to secrete aldosterone (Aldo). Two groups of normal conscious dogs were used in which plasma Na+ was independently elevated in the face of differing background levels of ANG II. In group 1 (n = 6), plasma Na+ was increased progressively over a 1-h period (from 143 +/- 1 to 152 +/- 1.2 meq/l), whereas plasma K+ was maintained at a constant level by intravenous infusion. With low background levels of ANG II (0.5 ng.kg-1.min-1), plasma Aldo remained unchanged with the increase in plasma Na+. With high ANG II (20.0 ng.kg-1.min-1), plasma Na+ changed in a similar manner (143.1 +/- 1.2 to 154.3 +/- 0.7 meq/l), whereas plasma Aldo decreased progressively from 35.3 +/- 2.3 to 27.9 +/- 3.8 ng/dl (P less than 0.05). In group 2 (n = 5), plasma Na+ was increased abruptly (144.9 +/- 0.6 to 152.1 +/- 0.5) and maintained at the elevated level for 3 h, and plasma K+ was held constant. Again, at low steady-state levels of ANG II (0.5 ng.kg-1.min-1), plasma Aldo levels remained unchanged. But, at intermediate levels of ANG II (5.0 ng-kg-1.min-1), producing plasma ANG II levels similar to those seen with dietary NaCl restriction, plasma Aldo decreased from 20.4 +/- 4.3 to 9.0 +/- 1.3 ng/dl (P less than 0.05). This rate of infused ANG II has been shown to result in plasma ANG II levels similar to that seen with dietary NaCl restriction. At the highest dose of ANG II (20 ng.kg-1.min-1), the ability of plasma Na+ to lower plasma Aldo was blunted to the extent that the decrease from 27.5 +/- 2.2 to 21.3 +/- 1.6 was not statistically significant. These studies indicate that physiological elevation of ANG II appears to sensitize the adrenal aldosterone responsiveness to changes in plasma Na+.

Adrenal Glands↗
PubMed1987

Chronic effects of vasopressin on fluid volume distribution in conscious dogs.

Previous studies have suggested that acute elevations of arginine vasopressin (AVP) may result in an extravascular to intravascular shift of fluid independent of any change in total body H2O (TBW). The present studies examined the chronic influence of elevated AVP on fluid volume distribution in five splenectomized, sodium-deprived conscious dogs (avg body wt = 18.9 +/- 0.7 kg). During 4 days of continuous intravenous AVP infusion (0.36 ng X kg-1 X min-1), the computerized average 24-h total body weight was maintained within 110 g of the control value by means of a sensitive servo-controlled scale device. Urine flow and urine osmolality averaged 335 +/- 52 ml/day and 637 +/- 36 mosmol/kg during the preinfusion period and changed to levels averaging 151 +/- 14 and 1,377 +/- 121 with elevated AVP (P less than 0.05). Chromium-51-labeled red cell volume (51Cr RBC), plasma volume (Evans blue), TBW (3H2O), calculated total blood volume (using 51Cr RBC and Hct), and mean arterial pressure averaged 22 +/- 1 ml/kg, 54 +/- 7 ml/kg, 0.62 +/- 0.04 l/kg, 68 +/- 3 ml/kg, and 99 +/- 3 mmHg, respectively, during the control period and remained unchanged during the AVP infusion period. Plasma protein, sodium, and osmolality averaged 6.4 +/- 0.1 g/dl, 145.7 +/- 0.8 meq/l, and 295.0 +/- 1.5 mosmol/kg during the preinfusion period and also remained unchanged with elevated AVP. We conclude from the present studies that AVP has minimal or no chronic influence on internal volume redistribution.

Animals↗
PubMed1986

Clinical experience with Mentor inflatable penile prosthesis in 206 patients.

The Mentor inflatable penile prosthesis (IPP) has been implanted in 206 patients with organic (95.2%) or psychologic (4.8%) impotency. The patients have been followed up for an average of 18.1 (4-42) months. A satisfactory result has been achieved in 98 per cent of these patients. A life analysis of the series shows that 88 per cent of all devices implanted will survive forty-two months without mechanical failure. One hundred sixty-four of these patients had not had previous penile surgery while 42 had had one or more penile prostheses implanted previously. The projected forty-two-month survival for the Mentor prosthesis in these subgroups is 94 per cent and 74 per cent, respectively. The improved life expectancy of the Mentor IPP, compared with the Scott IPP, is due to the superior durability of Mentor's polyurethane cylinders and to the increased reliability of the Mentor snap-on connector system. In this respect, there have been only one cylinder failure and 3 connector failures in the Mentor series. The connector failures occurred early in the series before the development of connector pliers; there have been no connector failures in the last 202 consecutive implantations. Wear-induced tubing leaks, the most common cause of device failure, occurred in 2.9 per cent of all implantations. Tubing failures were more common in patients who have had previous surgery, occurring in 9 per cent of salvage procedures and 1.3 per cent of primary implantations. The reason for the difference in tubing survival in virgin and salvage procedures is unknown; possibly the subcutaneous scar tissue present in secondary surgical procedures increases the chance of tubing segments touching and abrasing each other. Laboratory studies suggest that the nylon-reinforced tubing used in the manufacture of devices implanted since 1985 is more durable than is the standard silicone tubing used in the construction of devices implanted previously.

Adult↗
PubMed1986

Humoral control of water and electrolyte excretion during water restriction.

The goals of the present study were twofold: first, to assess the renal excretory and hormonal responses to chronic water restriction in dogs whose sodium retaining mechanisms had been stimulated through dietary sodium (Na+) deprivation; second, to determine the mediator(s) of the natriuresis which was observed with water restriction in these sodium deprived dogs. Three groups of dogs maintained on a low Na+ diet (5 mEq/day) for two weeks underwent a three day period of water restriction. In normal, intact dogs Group 1 (N = 5), water restriction resulted in a significant increase in Na+ excretion with a net cumulative loss of 26.3 +/- 2.6 mEq over three days. The natriuresis was associated with a significant increase in plasma vasopressin (PAVP) (1.7 to 10.2 pg/mliter) and a significant fall in plasma aldosterone (PALDO) from the levels observed with Na+ restriction alone (24.9 to 12.4 ng/dliter). The natriuresis could not be explained by decreases in food intake as determined by control studies in four dogs. Group 2 (N = 6) dogs had a decrease in PALDO with water restriction that was prevented by means of continuous i.v. aldosterone infusion (6.0 micrograms/kg/day). Dogs in this group failed to demonstrate a natriuresis during three days of water restriction, despite the fact that PAVP rose from 3.3 +/- 0.8 to a peak level of 14.95 +/- 1.9 pg/mliter. Group 3 (N = 6) dogs underwent selective neurohypophysectomy, thus preventing the rise in PAVP during three days of water restriction. In this group, PALDO also remained unchanged from the Na+ deprived level during water restriction, and no natriuresis was observed. We conclude: 1) that the natriuresis which occurs with water restriction is a potent physiological response that occurs even in the Na+ restricted state; and 2) this natriuresis can be explained by a fall in PALDO and not the rise in PAVP.

Aldosterone↗
PubMed1986

Osmoregulation during high salt intake: relative importance of drinking and vasopressin secretion.

Studies determined the relative contribution of drinking vs. vasopressin secretion in the regulation of extracellular osmolality in response to changes of Na intake. Daily Na intake was increased from 30 to 200 meq in dogs maintained under three conditions: normal dogs with ad libitum drinking, normal dogs with "fixed drinking," and neurohypophysectomized dogs with "fixed drinking" and vasopressin replaced by continuous infusion. (Drinking was fixed to that amount consumed during the normal Na control period.) The mechanisms of osmoregulation were highly nonlinear. As daily Na intake increased from 30 to 100 meq, renal natriuretic mechanisms predominated with only small contributions from either the thirst or vasopressin systems. At high levels of Na intake (200 meq/day), both drinking and vasopressin release contributed significantly to osmoregulation. The studies also determined that, in the absence of excess vasopressin secretion and increased drinking, plasma osmolality rose to nearly twice the levels as those observed in normal dogs that increased vasopressin secretion. We conclude that vasopressin-related renal conservation of water contributes to buffering the rise of osmolality when Na intake is increased without increased drinking. The studies also confirm that with available water to drink, the thirst mechanism together with renal Na excretory mechanisms are the predominant controllers of osmolality in situations of high sodium intake.

Animals↗
PubMed1986

Vasopressin responses to corticotropin releasing factor and hyperosmolality in conscious dogs.

We recently reported that ovine corticotropin releasing factor (CRF) infusion in conscious dogs elevated plasma vasopressin. The present study examines the vasopressin, adrenocorticotropic hormone (ACTH), and cortisol responses to CRF infusion (20 ng X kg-1 X min-1), to hypertonic saline infusion (NaCl 0.054 meq X kg-1 X min-1), and to simultaneous coinfusion of CRF and NaCl (CRF + NaCl) without (no-dex) or with (dex-treated) dexamethasone pretreatment in six conscious dogs (6-8 experiments/dog). CRF had no significant effect on plasma sodium or osmolality, blood pressure, or heart rate. NaCl increased plasma sodium from 146 +/- 1 to 151 +/- 1 meq/l and plasma osmolality from 298 +/- 3 to 305 +/- 3 mosmol/kg. Vasopressin increased significantly during CRF (2.1 +/- 0.5 to 4.8 +/- 1.1 pg/ml) and NaCl (1.9 +/- 0.3 to 5.0 +/- 0.8 pg/ml). Coinfusion of CRF and NaCl resulted in a response larger than the sum of the two infusions alone (3.0 +/- 1.6 to 31.4 +/- 18.5 pg/ml). The ACTH response to CRF (45 +/- 8 to 288 +/- 88 pg/ml) was not augmented by coinfusion with NaCl. DEX attenuated the vasopressin and ACTH responses to each infusion. We conclude that CRF-induced increases in vasopressin are augmented by a simultaneous osmotic stimulus. In addition, the plasma vasopressin responses to CRF and/or hypertonic saline infusion are inhibited by glucocorticoid pretreatment.

Adrenocorticotropic Hormone↗
PubMed1986

Chronic effects of vasopressin on plasma renin activity in sodium-restricted dogs.

The effects of chronic (4 days) arginine vasopressin (AVP) infusion were studied in two separate groups of animals: normal Na-restricted dogs with intact renal nerves (n = 8) and renal-denervated Na-restricted dogs (n = 5). Volume expansion during AVP infusion was prevented in these studies with a sensitive servo-controlled cage-scale system. With intravenous AVP infusion (0.36 ng X kg-1 X min-1), plasma AVP levels increased from nearly 3 to 15 pg/ml, whereas total body weight remained unchanged from the control level. In renal-innervated dogs, plasma renin activity (PRA) decreased significantly (P less than 0.05) from control levels of 5.50 +/- 0.61 to an average level of 3.45 +/- 0.76 ng angiotensin I (ANG I) X ml-1 X h-1 on days 1 and 2 of AVP infusion. Thereafter, PRA tended to remain decreased on days 3 and 4, averaging 3.82 +/- 1.02 ng ANG I X ml-1 X h-1, but this was not statistically significant. Urinary Na excretion and balance, however, were not significantly altered during the 4-day AVP infusion period. In renal-denervated dogs, the rise of PRA with Na restriction was 50% that seen in normal dogs. In this group, a transient suppression of PRA was observed on day 1 of AVP infusion from 2.84 +/- 0.75 to 1.46 +/- 0.47 ng ANG I X ml-1 X h-1. Urinary Na excretion increased transiently with a small net Na loss of 4.9 +/- 1.3 meq on day 2 of AVP infusion. No significant changes occurred in average 24-h mean arterial pressure (MAP) in response to AVP in either group of dogs. Thus, in contrast to our previous observations in Na-replete dogs, elevations of plasma AVP within the physiological range result in suppression of PRA, but for periods of no longer than 1-2 days in Na-restricted dogs. This decrease of PRA occurred in the absence of measurable changes in MAP, total body weight, or plasma catecholamines. In addition, this transient AVP-induced suppression of PRA was only partially blunted by prior renal denervation. Finally, in the Na-restricted dog, AVP appears to have minimal or no long-term effects on urinary Na excretion.

Aldosterone↗
PubMed1986

Are hypertensive effects of aldosterone, angiotensin, vasopressin, and norepinephrine chronically additive?

The effects of chronic combined administration of angiotensin II, norepinephrine, aldosterone, and arginine vasopressin were compared with the response to each of these hormones administered alone. The studies were performed in dogs to determine the extent to which moderately inappropriate elevations of these hormones could enhance each other's ability to produce chronic hypertension and influence Na and water homeostasis. Blood pressure sensitivity to Na intake was also evaluated by infusing the hormones for 11 days at normal levels of Na intake followed by 11 days at high Na intake with ad libitum drinking. Combined hormone administration did not enhance each hormone's singular hypertensive actions. With aldosterone infusion alone and normal Na intake, mean arterial pressure rose nearly 15 mm Hg and an additional 3 mm Hg during high Na intake. Combined hormone infusion also resulted in a nearly 15 mm Hg rise during normal Na intake and an additional 3 mm Hg rise in mean arterial pressure during high Na intake. Marked Na retention and hypernatremia were observed with aldosterone infusion, while hyponatremia characterized arginine vasopressin infusion. The combined hormone infusion resulted in a tendency toward hypernatremia, although daily Na balance was not significantly changed. Daily water turnover was substantially increased and urine osmolality fell to hypoosmotic levels, despite elevated arginine vasopressin levels. Even with high Na intake, dogs receiving either angiotensin II, arginine vasopressin, or norepinephrine at the same concentrations showed 4 to 10 mm Hg increases in mean arterial pressure. Thus, humoral summation or synergism of these hormones probably does not play a major role in the development of chronic hypertension.

Aldosterone↗
PubMed1986

Vasopressin excess: relative contribution of volume retention versus direct actions on renin secretion and sodium excretion.

Three groups of dogs were studied to determine to what extent the suppression of plasma renin activity (PRA), natriuresis, and hyponatremia, seen with chronic elevations of plasma vasopressin (AVP), were caused by volume expansion or some other more direct actions of AVP. The dogs of group 1 (n = 7) were infused with AVP (0.36 ng/kg/min, i.v.) for 2 weeks, while water intake was maintained at a constant level. The dogs of group 2 (n = 6) were permitted to drink ad libitum during AVP infusion. The dogs of group 3 (n = 7) were infused with AVP while total body weight and volume were maintained at a constant level by use of an electronically servocontrolled water infusion system. Group 1, with fixed water intake, retained a large fluid volume (1.4 L), with an associated 36 mm Hg rise in mean arterial blood pressure (MAP). Associated with this hypertension and increased volume were a suppression of PRA and substantial decreases in plasma sodium concentration with increased excretion of sodium. With ad libitum drinking (group 2), only mild volume expansion occurred, with no significant elevations of MAP or changes in sodium excretion. With a volume expansion of 300-400 ml, there was a significant decrease of PRA and plasma sodium concentration. Group 3, servocontrolled dogs, exhibited no change in MAP, plasma sodium concentration, or PRA throughout the 2-week period of AVP infusion. Sodium excretion was mildly elevated only on the first day of AVP infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The use of thoracic impedance for determining thoracic blood volume changes in man.

In these studies, strong inferential evidence is provided which suggests that thoracic impedance provides reliable estimates of thoracic blood volume changes in man. There were 24 volunteers studied in 4 different experiments. The results of these studies are as follows: Impedance derived blood volume changes in the calf of man correlate closely with standard estimates of calf blood volume changes made with strain gauge plethysmography. There is a close linear relationship between the increase of thoracic impedance and the increase of calf blood volume during head-up tilt. Volunteers who develop syncope during head-up tilt (presumably due to excessive decreases of central blood volume) demonstrate exaggerated increases of thoracic impedance. Decreases in central venous pressure produced by lower body negative pressure are significantly correlated to thoracic impedance increases.

Adult↗
PubMed1984

Mentor inflatable penile prosthesis. Preliminary clinical results in 30 patients.

The Mentor inflatable penile prosthesis was designed to decrease the incidence of mechanical failures associated with the Scott inflatable penile prosthesis. The penile cylinders of the Mentor prosthesis are manufactured from Bioflex polyurethane, a new polymer which is more durable and less elastic than silicone. The Mentor prosthesis also has a connector system which employs plastic clamps rather than suture ties to fix tubings to connectors. The new prosthesis has been implanted in 30 patients with organic impotency. These patients have been followed for an average of 7.7 (5-12) months. All patients achieved a satisfactory cosmetic and functional result from the procedure.

Aged↗
PubMed1984

Long-term blood pressure and metabolic effects of vasopressin with servo-controlled fluid volume.

Studies were performed in normal mongrel dogs (n = 8) to assess whether changes observed with chronic administration of vasopressin (AVP) were a result of direct actions of AVP or the consequence of changes in body fluid volume. AVP was infused continuously for 2 wk (0.36 ng X kg-1 X min-1 iv), while total body weight and body water (TBW) were maintained constant (+/- 50 g) using a servo-controlled system. A metabolic cage was mounted on sensitive force transducers for continuous monitoring of TBW. The summed voltage output of these transducers was used to servo control an intravenous infusion pump that adjusted the rate of water intake required for maintenance of a constant TBW. AVP infused under these conditions chronically increased plasma AVP levels from 2 to 22 pg/ml but resulted in no change of average 24-h mean arterial pressure, plasma sodium, or osmolality. Urine excretion decreased from 800 to 200 ml/day, whereas urine osmolality increased from 430 to 1,200 mosmol/kg and remained at these levels throughout the 2-wk AVP infusion. A net loss of 20 meq sodium occurred during the 1st day of AVP infusion but thereafter was unchanged. Plasma sodium and osmolality were unchanged from control during AVP infusions. We conclude that AVP-induced changes of arterial pressure, plasma sodium concentration and osmolality, renal escape, suppression of renin activity, and most of the observed natriuresis are events normally dependent on volume expansion.

Aldosterone↗
PubMed1984

Use of scrotal skin to cover cutaneous defects resulting from palliative lymph node dissections in groin and suprapubic area.

Scrotal skin was employed to cover skin defects resulting from palliative groin and suprapubic dissections designed to remove large masses of tumor which had eroded the skin. This technique provides a simple and effective alternative to more complex procedures using rotational skin and myocutaneous flaps to achieve primary skin closure in similar circumstances.

Aged↗