Renal hemodynamic effects of L-NAME during postnatal maturation in conscious lambs

The purpose of the present study was to investigate the effects of the L-arginine analogue, NG-nitro-L-arginine methyl ester, L-NAME, in modulating renal hemodynamics during postnatal maturation in conscious chronically instrumented lambs. To this end, renal hemodynamic responses to intravenous injection of 10, 20, and 40 mg/kg L-NAME, as well as its inactive enantiomer D-NAME, were measured for 4 h in conscious lambs approximately 1 week (n=10), 3 weeks (n=12), and 6 weeks (n=14) of age. Administration of L-NAME was associated with an increase in renal vascular resistance (RVR) leading to a decrease in renal blood flow. One-week-old lambs were more sensitive to the effects of L-NAME, a marked increase in RVR occurring after the smallest dose administered at 1 week but not at 3 and 6 weeks of age. Renal hemodynamic effects of L-NAME as well as the duration of the responses were also age dependent, such that changes in RVR were greatest and most prolonged in 1-week-old lambs. In addition, a smaller dose of L-NAME was required to attenuate acetylcholine-induced renal vasodilation in lambs aged 1 week compared with older animals. Our data provide new evidence to support the premise that endogenously produced nitric oxide plays a predominant role in regulating renal vascular tone early in life.

Age-dependent renal responses to the bradykinin B(2)- receptor antagonist icatibant in conscious lambs

To investigate the role of endogenously produced bradykinin in modulating renal function during postnatal maturation, various parameters of glomerular and tubular function were measured for 1 h before and after intravenous injection of 12.5 microg/kg of the specific B(2)-receptor antagonist icatibant to conscious, chronically instrumented lambs aged approximately 1 (n = 7) and approximately 6 wk (n = 7). In response to icatibant, and in the absence of any changes in renal hemodynamics, there was an approximately 80% decrease in glomerular filtration rate (GFR) at 20 min in 1-wk-old lambs that was sustained for 60 min; in 6-wk-old lambs, there was an approximately 70% decrease in GFR by 20 min, with control levels being reached by 40 min. Icatibant administration was also associated with significant decreases in urinary flow, Cl(-), and K(+) excretion rates that were similar in both groups of lambs, whereas Na(+) excretion decreased only in 6-wk-old lambs. We conclude that bradykinin modulates glomerular and tubular function in an age-dependent manner.

Prenatal exposure to nicotine impairs protective responses of rat pups to hypoxia in an age-dependent manner

Experiments were carried out on rat pups to investigate the interaction between prenatal exposure to nicotine and postnatal age on protective responses that promote survival during exposure to hypoxia. From days 6 or 7 of gestation, pregnant rats received either nicotine (approximately 6 mg of nicotine tartrate/kg of body weight per day) or vehicle continuously via a 28-day osmotic minipump. On postnatal days 1--2, 5--6 and 10--11, the pups were exposed either to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N(2) and 3% CO(2)) and their time to last gasp determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnea determined. Prenatal exposure to nicotine decreased the time to last gasp, but only in the 1--2-day-old animals. The total number of gasps was, however, increased in this age group due to the effect of nicotine on the gasping pattern. Furthermore, prenatal exposure to nicotine decreased the number of successful autoresuscitations and influenced the cardiorespiratory events preceding death in the 1--2- and 5--6-day-old pups but not in the 10--11-day-old pups. Thus, our experiments show that prenatal exposure to nicotine impairs protective responses of rat pups that may sustain life during exposure to hypoxia in an age-dependent manner.

Threshold levels of maternal nicotine impairing protective responses of newborn rats to intermittent hypoxia

Experiments were carried out to determine the threshold level of maternal nicotine that impairs protective responses of rat pups to hypoxia. From days 6 or 7 of gestation, pregnant rats received either vehicle or nicotine (1.50, 3.00, or 6.00 mg of nicotine tartrate. kg body wt(-1).day(-1)) or vehicle continuously via a subcutaneous osmotic minipump. On postnatal days 5 or 6, pups were exposed to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N(2) or 3% CO(2)) and their time to last gasp was determined, or they were exposed to intermittent hypoxia and their ability to autoresuscitate from hypoxic-induced primary apnea was determined. Perinatal exposure to nicotine did not alter the time to last gasp or the total number of gasps when the pups were exposed to a single period of hypoxia. The number of successful autoresuscitations on repeated exposure to hypoxia was, however, decreased in pups whose dams had received either 3.00 or 6.00 mg of nicotine tartrate/kg body wt; these dosage regimens produced maternal serum nicotine concentrations of 19 +/- 6 and 35 +/- 8 ng/ml, respectively. Thus our experiments define the threshold level of maternal nicotine that significantly impairs protective responses of 5- to 6-day-old rat pups to intermittent hypoxia such as may occur in human infants during episodes of prolonged sleep apnea or positional asphyxia.

Nitric oxide modulates arterial baroreflex control of heart rate in conscious lambs in an age-dependent manner

Experiments were carried out in conscious chronically instrumented lambs aged 1 (n = 6) and 6 wk (n = 5) to evaluate the arterial baroreflex control of heart rate (HR) during postnatal maturation and to investigate any modulatory role of endogenously produced nitric oxide (NO). Before and after intravenous administration of 20 mg/kg of the L-arginine analog N(G)-nitro-L-arginine methyl ester (L-NAME), the arterial baroreflex was assessed by measuring HR responses to increases and decreases in systolic arterial pressure achieved by intravenous administration of phenylephrine and sodium nitroprusside. The HR range over which the baroreflex operates and minimum HR as well as maximum gain were greater at 1 than at 6 wk of age. These age differences were abolished in the presence of L-NAME, which decreased the HR range and gain of the arterial baroreflex control of HR at 1 but not at 6 wk of age. These data provide new information that age-dependent effects of the arterial baroreflex appear to result from effects of endogenously produced NO.

Development and evaluation of a Research Project Program for medical students at the University of Calgary Faculty of Medicine

This essay outlines the development and evaluation of the Research Project Program (RPP) ten years after its introduction into the medical curriculum at the University of Calgary. The RPP consists of two mandatory for-credit courses. Students have the option of conducting either two smaller independent research projects or one larger project over the two years. At the end of the second-year course the students complete an evaluation of the RPP in which they are asked to assess and comment upon various aspects of the program. The authors compared data available from years one (the class of 1990) and ten (the class of 2000) and found significant differences between the two classes' approaches to the RPP. Most of the class of 2000 (89%) carried out two-year independent in-depth research projects spanning a wide range of topics. Half of these projects involved individual collection and analyses of data using experimental methods; this represented a 2.25-fold increase over the first year of the program. In the class of 2000, 44% of students presented their results at a newly implemented research symposium; an additional 22% of students presented their results at local, national, or international meetings. Further, 59% of the class of 2000 had either submitted or were planning to submit their research for peer-reviewed publication. In contrast, none of the students of the class of 1990 formally presented their research, and only 11% planned to submit their research findings for publication. The RPP has evolved in the ten years since its implementation, but the authors believe the program continues to foster independent learning and analytic and problem-solving skills.

Renal haemodynamic effects of B2 receptor agonist bradykinin and B2 receptor antagonist HOE 140 in conscious lambs

The present study was designed to test the hypothesis that the high renal vascular resistance characteristic of the newborn results from age-dependent changes in the responsiveness of the renal vasculature to kinins. Two studies were carried out in conscious, chronically instrumented lambs aged 1 and 6 weeks. Firstly, we measured the renal blood flow response to intra-arterial injection of the B2 receptor agonist bradykinin over the range of doses 0-800 ng x kg(-1). The ED50 renal blood flow response to bradykinin was 50 ng x kg(-1) in both age groups of lambs. Secondly, we measured the effects of intravenous administration of 12.5 microg x kg(-1) of the specific B2 receptor antagonist HOE 140; this dose attenuated the renal blood flow response to 50 ng x kg(-1) of bradykinin in both age groups. HOE 140 administration was associated with an age-dependent increase in mean arterial pressure, with little effect on heart rate or renal vascular resistance. This study provides new information regarding the effects of kinins in modulating renal haemodynamics during postnatal maturation. We reject our hypothesis and conclude that the high renal vascular resistance of the newborn does not appear to result from age-dependent changes in the responsiveness of the renal vasculature to endogenous kinins.

Chronic furosemide treatment alters renal responses to furosemide in conscious lambs

Despite the widespread chronic use of furosemide in the clinical management of a variety of fluid and electrolyte disorders in human infants, the physiological responses to furosemide in the newborn after chronic furosemide treatment are not known. The present experiments were conducted to determine the effects of chronic furosemide treatment on renal responses to acute furosemide challenge in conscious, chronically instrumented lambs. Experiments were carried out on day 1 (before chronic treatment) and on day 7 (after chronic treatment) in lambs given intravenous injections of either furosemide (1 mg/kg per 12 h for 5 days, n=9) or vehicle (0 mg/kg per 12 h for 5 days, n=4). Furosemide-treated animals responded to acute furosemide challenge on day 7 with attenuation of natriuresis and diuresis, and augmentation of kaliuresis compared with responses on day 1. Baseline renin production was elevated, although the renin response to furosemide was similar in chronic furosemide-treated and vehicle-treated lambs. Baseline aldosterone levels were not altered by chronic furosemide treatment, but the aldosterone response to acute furosemide injection was decreased after chronic furosemide treatment. Therefore, chronic furosemide treatment alters renal responses to furosemide in conscious lambs, and alters the aldosterone response to acute furosemide challenge.

Postnatal age influences the ability of rats to autoresuscitate from hypoxic-induced apnea

Failure to autoresuscitate from apnea by gasping has been suggested to have a role in sudden infant death. Little is known, however, about the factors that influence the ability of gasping to sustain life during acute hypoxia in the newborn. The present experiments were carried out on 105 rat pups to investigate the influence of postnatal age on the time to last gasp during a single hypoxic exposure and on the ability to autoresuscitate from primary apnea during repeated hypoxic exposures. On days 1-2, 5-6, 10-11, 15-16, and 19-20 postpartum, each pup was placed into a temperature-controlled chamber regulated to 37 +/- 1 degrees C and was exposed either to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N(2)-3% CO(2)), and the time to last gasp was determined, or repeated exposure to hypoxia was performed, and the ability to autoresuscitate from primary apnea was determined. Increases in postnatal age decreased the time to last gasp following a single hypoxic exposure and decreased the number of successful autoresuscitations following repeated hypoxic exposures. Thus our data provide evidence that postnatal age influences protective responses that may prevent death during hypoxia as may occur during episodes of prolonged sleep apnea.

Renin and heart rate responses to haemorrhage are age dependent in conscious lambs

The present experiments were carried out in conscious lambs (1-2 weeks old, n = 9) and older sheep (11-12 weeks old, n = 11) to determine whether the cardiovascular and endocrine responses to 0, 10 and 20 % haemorrhage were developmentally regulated. The major novel finding of our study is that throughout the first 3 months of postnatal life, there is a similar decrease in mean arterial pressure and a similar restoration of pressure to pre-haemorrhage levels, for the same degree of blood loss, yet the mechanisms used to restore pressure appear to be age dependent as follows. In lambs, but not in older sheep, heart rate increased for 1 h after 20% haemorrhage. Activation of the renin-angiotensin system was also greater and more prolonged in lambs than in older sheep following haemorrhage, and occurred at a lesser degree of blood loss. Plasma arginine vasopressin responses to haemorrhage were, however, similar in both age groups. These data provide new information that some of the mechanisms used to restore arterial pressure following blood volume depletion appear to be age dependent.

Acetylcholine chloride and renal hemodynamics during postnatal maturation in conscious lambs

To test the hypothesis that acetylcholine-induced relaxation of the renal artery decreases with postnatal age, we measured parameters of renal hemodynamics before and for 35 s after aortic suprarenal injection of acetylcholine in conscious, chronically instrumented lambs aged approximately 1 wk (n = 5) and approximately 6 wk (n = 5). Acetylcholine was administered in one of five doses ranging from 0 to 10 mg/kg body wt; doses were administered randomly, in the same volume. There were significant age- and dose-dependent changes in renal vascular resistance after acetylcholine administration, such that the response was greater in 1-wk-old lambs. After the highest dose tested, renal vascular resistance decreased by 13.6 +/- 7.3 (SD) mmHg. ml(-1). min. g kidney wt in 1-wk-old lambs and by 9.1 +/- 3.2 mmHg. ml(-1). min. g kidney wt in 6-wk-old lambs at 35 s. We also observed a transient renal vasoconstriction before the renal vasodilatation in 6-wk-old lambs but not in 1-wk-old animals. These data provide the first age- and dose-dependent effects of exogenous administration of acetylcholine on renal hemodynamics during maturation in conscious animals.

Dose-dependent effects of nitric oxide synthase inhibition on systemic and renal hemodynamics in conscious lambs

The present experiments were carried out to determine the role of nitric oxide in influencing systemic and renal hemodynamics in conscious young sheep. Parameters of cardiovascular function were measured before and for 4 h after intravenous injection of either L-NAME (NG-nitro-L-arginine methyl ester) or D-NAME (N(G)-nitro-D-arginine methyl ester) at doses of 10, 20, or 40 mg/kg in 13 conscious, chronically instrumented young sheep aged 43 +/-5 days. Blood pressure increased and heart rate decreased in a dose-dependent manner following administration of L-NAME. Renal vascular resistance was increased for 10 min following a dose of 10 mg/kg of L-NAME and for 120 min following a dose of 40 mg/kg of L-NAME. The renal vasodilatory response to close arterial injection of 1 microg/kg of acetylcholine was attenuated by L-NAME in a dose-dependent manner. These experiments provide the first information that under normal physiological conditions in conscious young animals, nitric oxide influences systemic and renal hemodynamics.

Perinatal nicotine exposure impairs ability of newborn rats to autoresuscitate from apnea during hypoxia

Failure to autoresuscitate by hypoxic gasping during prolonged sleep apnea has been suggested to play a role in sudden infant death. Furthermore, maternal smoking has been repeatedly shown to be a risk factor for sudden infant death. The present experiments were carried out on newborn rat pups to investigate the influence of perinatal exposure to nicotine (the primary pharmacological and addictive agent in tobacco) on their time to last gasp during a single hypoxic exposure and on their ability to autoresuscitate during repeated exposure to hypoxia. Pregnant rats received either nicotine (6 mg. kg-1. 24 h-1) or vehicle continuously from day 6 of gestation to days 5 or 6 postpartum via an osmotic minipump. On days 5 or 6 postpartum, pups were exposed either to a single period of hypoxia (97% N2-3% CO2) and their time to last gasp was determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnea was determined. Perinatal exposure to nicotine did not alter the time to last gasp, but it did impair the ability of pups to autoresuscitate from primary apnea. After vehicle, the pups were able to autoresuscitate from 18 +/- 1 (SD) periods of hypoxia, whereas, after nicotine, the pups were able to autoresuscitate from only 12 +/- 2 periods (P < 0.001) of hypoxia. Thus our data provide evidence that perinatal exposure to nicotine impairs the ability of newborn rats to autoresuscitate from primary apnea during repeated exposure to hypoxia, such as may occur during episodes of prolonged sleep apnea.

Renal denervation alters cardiovascular and endocrine responses to hemorrhage in conscious newborn lambs

To investigate the role of renal sympathetic nerves in modulating cardiovascular and endocrine responses to hemorrhage early in life, we carried out three experiments in conscious, chronically instrumented lambs with intact renal nerves (intact; n = 8) and with bilateral renal denervation (denervated; n = 5). Measurements were made 1 h before and 1 h after 0, 10, and 20% hemorrhage. Blood pressure decreased transiently after 20% hemorrhage in intact lambs and returned to control levels. In denervated lambs, however, blood pressure remained decreased after 60 min. After 20% hemorrhage, heart rate increased from 170 +/- 16 to 207 +/- 18 beats/min in intact lambs but not in denervated lambs, in which basal heart rates were already elevated to 202 +/- 21 beats/min. Despite an elevated plasma renin activity (PRA) measured in denervated (12.0 +/- 6.4 ng ANG I . ml-1 . h-1) compared with intact lambs (4.0 +/- 1.1 ng ANG I . ml-1 . h-1), the increase in PRA in response to 20% hemorrhage was similar in both groups. Plasma levels of arginine vasopressin increased from 11 +/- 8 to 197 +/- 246 pg/ml after 20% hemorrhage in intact lambs but remained unaltered in denervated lambs from baseline levels of 15 +/- 10 pg/ml. These observations provide evidence that in the newborn, renal sympathetic nerves modulate cardiovascular and endocrine responses to hemorrhage.

Dose-dependent cardiovascular, renal, and endocrine effects of furosemide in conscious lambs

In recent experiments in conscious lambs, we showed that in addition to its well-known natriuretic and diuretic effects, i.v. injection of 2 mg/kg of furosemide resulted in a sustained increase in heart rate and an age-dependent increase in plasma renin activity. To determine whether these responses were dose dependent, we measured various parameters of cardiovascular, renal, and endocrine function in six chronically instrumented lambs. Three of seven doses of furosemide were tested at 48-h intervals; the range of doses was 0 to 7.5 mg/kg. A dose-dependent transient pressor response occurred within 20 min of furosemide administration; the duration of this response increased with increasing doses. Heart rate increased 40 min after doses of furosemide > or = 0.25 mg/kg; this response was not dose dependent. Renin increased following all doses; the peak and the duration of the renin response were dose dependent. These data provide new information on the dose-dependent cardiovascular, renal, and endocrine responses to furosemide in conscious newborn lambs.

Endocrine effects of pregnancy and exposure to a simulated open field in rats

In adult rats, exposure to a novel environment, such as a simulated open field, elicits an increase in body core temperature. We have recently shown that this response is attenuated in midpregnancy and abolished at term of pregnancy in rats. We postulated that this gestation-dependent response resulted from alterations in the hypothalamic-pituitary-adrenal axis. To test this hypothesis, we measured the effects of pregnancy on renin, corticosterone, and arginine vasopressin (AVP) responses to exposure to either a simulated open field (30 or 120 min) or to the home cage (30 or 120 min) in rats. Pregnancy increased renin and corticosterone levels but not plasma AVP levels. Exposure to an open field decreased renin and increased plasma AVP levels in nonpregnant rats and on days 15 and 20 of gestation in pregnant rats, compared with home cage responses. Serum corticosterone levels were elevated after exposure to an open field in nonpregnant and pregnant rats, compared with home cage rats, the effect being more prolonged on day 20 of gestation. These observations provide new information on endocrine changes during pregnancy in rats and may help to explain the attenuated stress-induced hyperthermic response to exposure to a novel environment seen near term of pregnancy.

Effects of renal denervation on cardiovascular and renal responses to ACE inhibition in conscious lambs

Effects of renal denervation on cardiovascular and renal responses to ACE inhibition in conscious lambs. J. Appl. Physiol. 83(2): 414-419, 1997.-Cardiovascular and renal effects of either the angiotensin-converting enzyme inhibitor captopril or vehicle were measured in chronically instrumented lambs in the presence (intact; n = 6) and absence of renal sympathetic nerves (denervated; n = 5) to determine whether there was an interaction between the renin-angiotensin system and renal sympathetic nerves early in life. Captopril caused a similar decrease in mean arterial pressure (P < 0. 001) in intact and denervated lambs, predominantly through a decrease in diastolic pressure. Heart rate was increased from 177 +/- 34 to 213 +/- 22 (SD) beats/min during captopril compared with vehicle infusion in intact lambs. In denervated lambs, basal heart rates were elevated to 218 +/- 33 beats/min; there was no further increase in heart rate during captopril compared with vehicle infusion. Captopril infusion caused a decrease in renal vascular resistance but only in the absence of renal nerves. These findings provide evidence to suggest that early in life there is an interaction between renal sympathetic nerves and the renin-angiotensin system in regulating renal hemodynamics and the baroreflex control of the heart.

Systemic and renal hemodynamic effects of hemorrhage in conscious lambs

The purpose of the present study was to investigate the systemic and renal hemodynamic effects of hemorrhage in the newborn to determine whether the newborn is capable of restoring blood pressure in the face of blood loss at hemorrhage of up to 20% of vascular volume. Experiments were carried out in conscious, chronically instrumented lambs and consisted of measurements before, during, and after hemorrhage at 0 (n = 9), 10 (n = 8), 15 (n = 8), and 20% (n = 8) of blood volume. Right atrial pressure decreased but only after 20% hemorrhage. There was a transient decrease in blood pressure at 10-15% hemorrhage and a sustained decrease in blood pressure after 20% hemorrhage (from 82 +/- 7 to 66 +/- 9 mmHg). Heart rate increased transiently after 15% hemorrhage (from 173 +/- 32 to 204 +/- 66 beats/min); heart rate remained increased for 60 min after 20% hemorrhage from 171 +/- 17 to 214 +/- 31 beats/min. There were no changes in renal vascular resistance in response to hemorrhage of up to 20% of vascular volume. These observations provide evidence that the newborn is capable of buffering blood pressure in response to blood loss of up to 20% of vascular volume and that the renal bed does not appear to contribute to the restoration of blood pressure after blood loss early in life.

Effects of the angiotensin converting enzyme (ACE) inhibitor, captopril, on the cardiovascular, endocrine, and renal responses to furosemide in conscious lambs

To test the hypothesis that angiotensin II modulates the physiological responses to furosemide in the newborn, various parameters of cardiovascular, renal, and endocrine function were measured before and after iv injection of furosemide to eight conscious, chronically instrumented lambs in the presence and absence of the angiotensin converting enzyme (ACE) inhibitor, captopril. During ACE inhibition, the rise in heart rate and decrease in renal blood flow in response to furosemide did not occur, and the natriuretic and diuretic responses to furosemide were attenuated by approximately two-thirds. There was also an increase in the urinary excretion of prostaglandin F2 and prostaglandin F1 alpha as well as an increase in the excretion of prostaglandin E2 after furosemide, in the presence of ACE inhibition. Therefore, the cardiovascular, renal, and endocrine responses to furosemide in conscious lambs were significantly altered by ACE inhibition.

Renal nerves do not modulate the renal and endocrine responses to furosemide in conscious lambs

To test the hypothesis that renal sympathetic nerves influence the renal and renin responses to furosemide in conscious newborn animals, experiments were carried out in chronically instrumented lambs with either bilateral renal denervation (denervated, n = 7, age = 13 +/- 3 (SD) days) or intact renal sympathetic nerves (intact, n = 6, age = 13 +/- 4 (SD) days), at least 4 days after surgery. Basal glomerular filtration rate (GFR), urinary flow, and sodium excretion rates were similar in intact and denervated lambs (p > 0.5). A prompt diuretic and natriuretic response and a decrease in GFR occurred after i.v. furosemide (2 mg/kg); these responses were similar in intact and denervated lambs. Basal plasma renin activity (PRA) was not altered by renal denervation. PRA increased 10 min after furosemide (p < 0.001) and remained elevated at 90 min; the response was similar in both groups of lambs. Basal plasma aldosterone levels were elevated in denervated (191 +/- 232 (SD) pg/mL) compared with intact lambs (62 +/- 24 (SD) pg/mL). Plasma aldosterone levels increased after furosemide administration in both groups of animals. These data provide evidence to suggest that renal sympathetic nerves do not appear to modulate the renal and endocrine responses to furosemide, at least at a dose of 2 mg/kg. Our observations also support the premise that early in life, aldosterone counteracts the effects of renal denervation on fluid and electrolyte homeostasis.

Cardiovascular, renal, and endocrine responses to graded volume expansion in lambs during maturation

To further investigate the maturation of the cardiopulmonary baroreflex, we measured the effects of a 45-min blood volume expansion to an increase in right atrial pressure of approximately 4 mmHg in chronically instrumented newborn (n = 17) and older lambs (n = 14). Measurements included various parameters of endocrine, cardiovascular, and renal function and concomitant recording of renal sympathetic nerve activity (RSNA). During blood volume expansion, RSNA was inhibited to a similar extent in newborns and older lambs when atrial pressures were increased by approximately 4 mmHg. A sympathoinhibition persisted in newborns but was only transient in older lambs. In newborn lambs, heart rate decreased in response to blood volume expansion, whereas heart rate remained constant after blood volume expansion in older lambs. The renal and endocrine responses to blood volume expansion were, however, similar in newborns and older lambs. These data provide evidence that when atrial pressures are matched, the renal and endocrine responses to blood volume expansion are similar, but there are differential cardiovascular and RSNA responses. Any reduced ability of the newborn kidney to excrete a volume load is therefore probably related to maturational differences in its distribution between the capacitance vessels and the heart.

Met-enkephalin Arg-Phe-immunoreactive neurons in the central nervous system of the pond snail Lymnaea stagnalis

The distribution of an opioid peptide related to YGGFMRF was determined in the CNS and other organs of the pond snail, Lymnaea stagnalis, by RIA and immunocytochemistry. RIA revealed the highest levels in the CNS (1 pmol/organ) and penis (400 fmol/organ). There were also significant levels in the haemolymph, most of which was not associated with haemocytes (580 fmol/ml). Both serial section and whole-mount immunocytochemistry of the CNS revealed immunoreactive cells in every ganglion with the majority in the cerebral and pedal ganglia. In the pedal ganglia some of the immunoreactive cells were close to the cells of the A-cluster, which are known to respond to opioids, and could innervate them. In the cerebral ganglia the immunoreactive cells included a group of neurosecretory cells, the caudo dorsal cells (CDCs) and the terminals of these cells in the cerebral commissure were also stained. The CDCs secrete peptides into the haemolymph and so could be the source of the YGGFMRF immunoreactivity. Immunoreactivity (including the CDCs) was observed in locations that correspond to those reported for other fragments of proenkephalin, such as Met- and Leu-enkephalin, suggesting that they may share a common precursor, a Lymnaea proenkephalin. A map of the 358 YGGFMRF-immunoreactive cells in the CNS is presented, many of which have not been previously identified.

Effects of renal denervation on cardiovascular response to furosemide in conscious lambs

The cardiovascular response to furosemide in the newborn and the role of renal sympathetic nerves in influencing this response have not been investigated. We hypothesized that in conscious lambs, furosemide would decrease blood pressure, the response being accentuated in the absence of renal sympathetic nerves. Pulsatile pressures and heart rates were measured before and after furosemide (2 mg/kg) administration to chronically instrumented lambs with either bilateral renal denervation (denervated, n = 8) or renal nerves intact (intact, n = 6). In intact lambs, mean arterial pressure remained constant after furosemide; in denervated lambs there was an increase in arterial pressure 20 min after furosemide (P < 0.001), and control levels were reached by 100 min. Basal heart rate was higher in denervated than in intact lambs (P = 0.009). In both groups of lambs, heart rate increased 40 min after furosemide and remained elevated. These data provide new information that, in conscious newborn animals, renal sympathetic nerves influence the blood pressure response to furosemide, as well as basal control of heart rate.

Renal and renin responses to furosemide in conscious lambs during postnatal maturation

Despite the widespread use of furosemide in the treatment of various fluid and electrolyte disorders in the preterm and term human infant and child, the physiological effects of this potent diuretic agent on renal function and renin release during postnatal maturation are poorly understood. To test the hypothesis that the renal and renin responses to furosemide are altered during postnatal maturation, experiments were carried out in conscious chronically instrumented newborn lambs (11 +/- 3 days, n = 7) and older lambs (28 +/- 3 days, n = 6), at least 5 days after surgery under halothane anesthesia for placement of catheters. Renal function and plasma renin activity (PRA) were measured for 1 h before and 2 h after intravenous injection of furosemide (2 mg/kg; 0.2 mL/kg) or vehicle (0.2 mL/kg). Glomerular filtration rate (GFR) decreased after furosemide administration to both groups of lambs. However, the time course of this decrease in GFR was different, occurring sooner in older lambs (30 min) than in newborns (90 min). GFR remained significantly decreased after 150 min in both age-groups. The natriuretic and diuretic responses to furosemide were similar in newborns and older lambs, peak diuretic and natriuretic responses occurring within 30 min. PRA increased dramatically in both age-groups after furosemide; the response was accentuated in newborns. After 2 h, PRA was still elevated in newborns but returned towards control levels in older lambs. These data demonstrate that both the GFR and renin responses to furosemide are altered during ontogeny.

Evaluation of two opioid-acetaminophen combinations and placebo in postoperative oral surgery pain

STUDY OBJECTIVE

To determine the relative analgesic potency and adverse effect liability of hydrocodone bitartrate 7.5 mg with acetaminophen 500 mg, codeine phosphate 30 mg with acetaminophen 300 mg, and placebo in the treatment of pain following oral surgery.

DESIGN

Randomized, double-blind, single-dose, placebo-controlled, parallel-group study with self-ratings at 30 minutes and then at hourly intervals from hour 1 to hour 6.

SETTING

Private, oral surgery practice sites.

PATIENTS

Three hundred twenty-four outpatients with moderate or severe pain after the surgical removal of impacted third molars were selected. One was lost to follow-up and 32 did not need an analgesic; 232 patients had valid efficacy data.

INTERVENTIONS

Patients were treated with a single oral dose of hydrocodone bitartrate 7.5 mg with acetaminophen 500 mg, codeine phosphate 30 mg with acetaminophen 300 mg, or placebo when they experienced steady, moderate or severe pain that, in their opinion, required an analgesic. Using a self-rating record, subjects rated their pain and its relief for 6 hours after medicating; estimates of peak and total analgesia were derived from these subjective reports.

MEASUREMENTS AND MAIN RESULTS

This study was a valid analgesic assay. Both active treatments were significantly superior to placebo for all measures of analgesic efficacy. The hydrocodone-acetaminophen combination was significantly superior to the codeine-acetaminophen combination for total pain relief and the number of evaluations with 50% relief. Both active treatments manifested an analgesic effect within 30 minutes; the effect persisted for 5 hours for the codeine combination and 6 hours for the hydrocodone combination. Adverse effects were transient, consistent with the pharmacologic profiles of opioids, and none required treatment.

CONCLUSIONS

A slight advantage in analgesic efficacy was demonstrated in this single-dose study for the hydrocodone-acetaminophen combination. Repeat-dose studies, however, should be conducted to determine the clinical significance of the difference in analgesic effect of these opioid combinations.

Functional morphology of the light yellow cell and yellow cell (sodium influx-stimulating peptide) neuroendocrine systems of the pond snail Lymnaea stagnalis

Neuroendocrine light yellow cells of the pond snail Lymnaea stagnalis express a neuropeptide gene encoding three different peptides. The morphology of the cell system has been studied by in situ hybridization, using two synthetic oligonucleotides encoding parts of light yellow cell peptides I and III, and by immunocytochemistry with antisera to synthetic light yellow cell peptide II and to two fragments of light yellow cell peptide I. One large cluster of light yellow cells was observed in the ventro-lateral protrusion of the right parietal ganglion, smaller clusters lying in the posterior dorsal part of this ganglion and in the visceral ganglion. The cells had an extended central neurohaemal area. Immunopositive axons projected into all nerves of the ganglia of the visceral complex, into the superior cervical and the nuchal nerves, and into the connective tissue surrounding the central nervous system. Axon tracts ramified between the muscle cells of the walls of the anterior aorta and of smaller blood vessels. Peripheral innervation by the light yellow cell system was only found in muscular tissue of the ureter papilla. The antisera to the two peptide fragments of light yellow cell peptide I not only stained the light yellow cells, but also the identified yellow cells, which have previously been shown to produce the sodium influx-stimulating neuropeptide. The latter cells were negative to the in situ hybridization probes and antisera specific to the light yellow cell system. It is therefore unlikely that the yellow cells express the light yellow cell neuropeptide gene. Nevertheless, the cells contain a neuropeptide sharing antigenic determinants with light yellow cell peptide I.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation between PCNA and AgNOR scores in non-Hodgkin's lymphomas using sequential staining technique

AIMS

To investigate the relation between the numbers of interphase silver stained nucleolar organiser regions (AgNORs) and immunolabelling with the monoclonal antibody PC10, which demonstrates proliferating nuclei by reacting with proliferating cell nuclear antigen (PCNA).

METHODS

The established sequential technique for the demonstration of interphase AgNORs and of antigens in paraffin wax sections was applied to a small series of non-Hodgkin's lymphomas (NHL) of both low and high grade type, together with specimens of palatine tonsil. The numbers of PCNA positive cells were counted in all specimens; in the tonsils the cells were counted in both follicle centres and in the interfollicular areas. The numbers of AgNORs in both PCNA positive and PCNA negative nuclei were then counted.

RESULTS

Lower numbers of PCNA positive cells were found in the low grade than the high grade NHL (18-28.4% and 34.2-51.3%, respectively). This was reflected in the two areas of the palatine tonsils, the counts being higher in the follicle centre nuclei than in those in the interfollicular compartments. In general, the numbers of AgNORs were higher in the PCNA positive nuclei than in those lacking the antigen; however, a consistent finding was that relatively high AgNOR scores were observed in PCNA negative nuclei, especially in the high grade lymphomas. In the tonsils, however, the AgNOR counts were much lower in the nuclei lacking PCNA than in those containing it.

CONCLUSIONS

The results obtained in the lymphomas were rather unexpected as, in general, previous studies have shown a close direct or indirect relation between AgNOR scores and proliferating cell counts. An explanation for these findings may be that the argyrophil proteins associated with proliferating cells remain in the nucleus in detectable form longer than the PCNA antigen, at least in neoplastic tissue.

Ontogeny of renal response to specific dopamine DA1-receptor stimulation in sheep

The present study was designed to characterize the developmental changes in the renal responses to dopamine DA1-receptor activation in chronically instrumented preterm (109-115 days) and near-term (130-140 days, full term 145 days) fetal sheep. Cumulative doses of the selective DA1-agonist fenoldopam increased mean arterial blood pressure (MABP) in both preterm (+16 +/- 3%) and near-term fetuses (+16 +/- 3%) but had no significant effect on renal blood flow velocity. Infusion of the DA1-antagonist SCH-23390 did not affect the increase in MABP, suggesting that the effect of fenoldopam on MABP was not directly related to activation of DA1-receptors. Fenoldopam infusion had no significant effects on renal function parameters in preterm fetuses. In near-term fetuses, however, fenoldopam increased urinary flow rate (82.6 +/- 20.9%, P < 0.003), glomerular filtration rate (GFR; 16.6 +/- 4.9%, P < 0.01), urinary sodium excretion (40.1 +/- 14.9%, P < 0.02), and fractional excretion of sodium (26.8 +/- 11.2%, P < 0.03). Infusion of the DA1-antagonist SCH-23390 blocked the fenoldopam-induced diuresis and natriuresis but had no significant effect on the rise in GFR. Fenoldopam infusion had no significant effects on plasma renin activity and plasma aldosterone concentration and on urinary prostaglandin (PG) excretion (PGE2, PGF2 alpha, and 6-keto-PGF1 alpha). Taken together, these results suggest that the renal effect of DA1-receptor activation is age dependent and that stimulation of DA1-receptor in near-term fetuses is associated with a diuresis and natriuresis that seem to be independent of renal hemodynamics and adrenal effects.

Renal nerves modulate kidney renin gene expression during the transition from fetal to newborn life

The role of renal nerves in regulating changes in plasma renin activity (PRA) and renal renin gene expression was studied in intact (n = 6) and denervated (n = 6) fetal sheep before birth and during the first 24 h after delivery. Renal denervation completely blunted the rise in PRA observed 24 h after delivery in newborn lambs; in lambs with intact kidneys, PRA increased significantly (P less than 0.05) from 3.26 +/- 0.60 (predelivery) to 6.34 +/- 1.85 ng angiotensin I (ANG I).ml-1.h-1 (24 h postdelivery), while in lambs with denervated kidneys, predelivery and post-delivery values were 2.84 +/- 0.19 and 2.49 +/- 0.45 ng ANG I.ml-1.h-1, respectively. Renin mRNA levels were significantly lower (P less than 0.001) in denervated than in intact kidneys 24 h after birth. A close analysis of these results also revealed that renin mRNA levels were significantly higher (P less than 0.001) in intact kidneys of newborn lambs delivered vaginally (n = 3) than in newborn lambs delivered by cesarean section (n = 3). These results suggest that renal nerves play an important role in regulating renin gene expression and PRA during the transition from fetal to newborn life.

Effects of volume expansion on renal sympathetic nerve activity and cardiovascular and renal function in lambs

To assess the cardiopulmonary baroreflex in the immature animal, effects of volume expansion on changes in right atrial pressure, renal sympathetic nerve activity, and renal function were measured in chronically instrumented newborn (4-8 days; n = 13) and older lambs (4-5 wk; n = 14). Studies were carried out for 30 min before and 2 h after volume expansion with 6% Dextran 70 (25 ml/kg). Right atrial pressure increased by 4.0 +/- 0.5 mmHg in newborns and by 8.8 +/- 0.6 mmHg in older lambs within 15 min of volume expansion (P less than 0.001). After volume expansion, heart rate decreased in newborns from 237 +/- 6 beats/min to a nadir of 211 +/- 7 beats/min 2 h later (P less than 0.001) but remained constant at control levels of 148 +/- 9 beats/min in older lambs. Maximal inhibition of renal sympathetic nerve activity was achieved at 15 min in older lambs (-50.1 +/- 7.5%) and at 60 min (-58.3 +/- 10.9%) in newborns in which there was a prolonged sympathoinhibition (P less than 0.001). There was also a significant diuretic response in both groups but a limited natriuretic response to volume expansion in newborns (P greater than 0.05) compared with older lambs (P less than 0.001). These data demonstrate the presence of the cardiopulmonary baroreflex in the first week of life in lambs. The sustained sympathoinhibition and bradycardia seen in response to volume expansion in newborns but not in older lambs support the hypothesis that the reflexes controlling arterial pressure and blood volume change with postnatal maturation.

Mechanisms regulating renal sodium excretion during development

The present review focuses on the ontogeny of mechanisms involved in renal sodium excretion during renal maturation. The effect of birth on renal excretion of sodium and the role played by the different tubular segments in the regulation of sodium excretion during maturation are discussed. The influence of circulating catecholamines and renal sympathetic innervation in regulating sodium excretion during renal development is reviewed. The effects of aldosterone, atrial natriuretic factor, and prostaglandins on sodium regulation during renal maturation are discussed. Special emphasis is given to the potential role of glucocorticoids in modulating sodium excretion early in life.

Analgesic efficacy of bromfenac, ibuprofen, and aspirin in postoperative oral surgery pain

We recently demonstrated that 25 mg of bromfenac, a new nonsteroidal anti-inflammatory analgesic, is at least as effective as 400 mg of ibuprofen in relieving postoperative oral surgery pain. Our objective in this study was to determine whether higher doses were significantly more effective. Two hundred eighty (280) outpatients with postoperative pain after the surgical removal of impacted third molars were randomly assigned, on a double-blind basis, a single oral dose of 10, 25, 50, or 100 mg bromfenac; 650 mg aspirin; 400 mg ibuprofen; or placebo. Subjects rated their pain and its relief for 8 hours. All active treatments were significantly superior to placebo, and bromfenac and ibuprofen were significantly superior to aspirin. The slope of the dose-response curve of bromfenac was significant. The 100 mg bromfenac dose was significantly more effective than the 400 mg ibuprofen dose and had a significantly longer duration of analgesic action.

Regulation of sodium metabolism and extracellular fluid volume during development

In addition to regulating developmental changes in body fluid content, the newborn kidney must maintain a positive sodium balance to ensure adequate body growth. Mechanisms by which the developing organism perceives changes in volume and the manner in which the kidney responds to these changes have been reviewed. Perception of changes in ECF volume is sensed by volume receptors that involve central nervous system signal processing (e.g., low- and high-pressure volume receptors) before influencing the kidney by way of the renal nerves or that are directly coupled with the kidney and do not involve central nervous system processing (e.g., juxtaglomerular apparatus, ANF, hepatic factors). Results presently available demonstrate that these mechanisms are functional early in life and that their sensitivity changes during development in accordance with the needs of the organism. In addition, the developing kidney has unique characteristics that allow it to maintain a positive sodium balance necessary for growth.

Role of renal sympathetic nerves in lambs during the transition from fetal to newborn life

To determine the role of renal sympathetic nerves in influencing renal function during the transition from fetal to newborn life, studies were carried out in conscious, chronically instrumented fetal sheep with either bilateral renal denervation (n = 11) or intact renal nerves (n = 12), 3-6 d after surgery. Endocrine, renal, and cardiovascular parameters were measured before and after delivery of lambs by cesarean section. Blood pressure and heart rate were similar in intact and denervated fetuses, and increased after delivery in both groups. There was also a transient diuresis and natriuresis, in the immediate postnatal period, the response being significantly greater in denervated than intact lambs (P less than 0.05). By 24 h postnatally, fluid and electrolyte excretions were similar in both groups, and significantly less than fetal levels. In the absence of renal nerves, the normal rise in plasma renin activity at birth was attenuated. These data provide evidence that renal sympathetic nerves play an important role during the transition from fetal to newborn life, and support the premise that birth is associated with sympathetic activation.

Endocrine effects of ventilation, oxygenation and cord occlusion in near-term fetal sheep

The transition from fetal to newborn life is associated with significant endocrine changes. Some of these changes may be triggered by the effects of spontaneous respiration, increased oxygenation and removal of the placental circulation at birth. We, therefore, studied endocrine function during in utero ventilation, oxygenation and cord occlusion, in nine chronically-instrumented fetal sheep aged 137 to 140 days of gestation. During the sequential effects of in utero ventilation and oxygenation, plasma renin activity (PRA) and angiotensin II (AII) remained at control levels of 6.3 +/- 1.9 ng/ml per h and 66 +/- 15 pg/ml. After cord occlusion, PRA increased to 10.3 +/- 2.2 ng/ml per hr and AII increased to 86 +/- 24 pg/ml, the latter being non-significant. Plasma cortisol levels also increased from control levels of 3.5 +/- 1.0 to 6.7 +/- 0.8 g/dl during cord occlusion (P = 0.02). During the sequential effects of ventilation, oxygenation and cord occlusion, plasma epinephrine increased from control levels of 87 +/- 17 to 492 +/- 142 pg/ml (P = 0.04), and plasma norepinephrine levels increased slightly from 620 +/- 112 to 850 +/- 214 pg/ml. These data provide evidence that many of the changes in endocrine function seen at birth result from factors other than spontaneous respiration, oxygenation and umbilical cord occlusion.

Zinc absorption in women: comparison of intrinsic and extrinsic stable-isotope labels

Fractional absorption of extrinsic and intrinsic zinc from milk-based formulated diets was measured in 10 young women by using a simultaneous triple-isotope method based on fecal monitoring of unabsorbed enriched stable-isotope labels. Zinc intake was held nearly constant (mean zinc intake = 1.48 mumol.kg body wt-1.d-1) throughout the 18-d controlled feeding phase of the study by addition of extrinsic 64Zn to all formula feedings, with substitution of the extrinsic 67Zn label for some of the 64Zn when formula intrinsically labeled with 70Zn was given. Fractional absorption values of intrinsic and extrinsic zinc labels, 0.267 +/- 0.092 (mean +/- SD) and 0.282 +/- 0.086, respectively, were highly correlated (r = 0.83, P less than 0.05) and did not differ significantly. The ratio of fractional absorption of the extrinsic to that of the intrinsic label, 1.08 +/- 0.20 (mean +/- SD), was not significantly different from unity. The results show that extrinsic labeling by use of enriched stable isotopes is a valid means of determining zinc absorption from milk-based diets in adult humans.