Water movements after an intraruminal water load in pregnant and lactating Sardi sheep

The effects of an intraruminal load of 3 litres of water on body water movements was compared in Sardi sheep during the last month of pregnancy, lactation and a non-pregnant, non-lactating control period. Before the water load, rumen fluid volume, estimated by polyethylene glycol was similar in pregnant, compared to control, animals and 27% higher in lactating sheep. After the water load, rumen volume returned to pre-hydration level in 1 h during pregnancy, after 3 h during lactation and in the control period. Rumen osmolality decreased by 40% and remained at this low level for 3 h after the water load in all physiological periods. When the water load was tritiated water (TOH), the rate of TOH transfer into plasma was faster during the last month of pregnancy than during the control period. Plasma osmolality and proteins decreased in response to the water load. No differences in these responses were observed between pregnancy, lactation and the control period. Water diuresis began in the first 30 min following the water load in pregnant ewes and in the second 30 min in lactating and control ewes. The diuresis was also more pronounced in pregnant, than in non-pregnant, states. These results indicate that water is more rapidly absorbed from the gastrointestinal tract in pregnant, rather than in non-pregnant, sheep. This may partly explain the increased water turnover seen during pregnancy.     

Effect of dietary energy intake on tubular reabsorption of urea in sheep

The aim of the experiment was to determine the effect of dietary energy intake on renal urea excretion in sheep with different nitrogen intakes. The control sheep, with a high nitrogen and energy intake, were given a daily feed dose of 21.18 g N and 15.2 MJ digestible energy (DE). The two experimental groups, with an equal, low nitrogen intake, were given diets with a different energy content. The high energy diet contained 3.63 g N and 14.18 MJ DE, the low energy diet 3.4 g N and 6.44 MJ DE. After nine weeks' adaptation to the diets, renal functions were measured by a standard clearance technique. It was found that, under stable urine flow conditions, both groups given the low nitrogen diet had a significantly lower glomerular filtration rate, fractional urea excretion and total urea excretion. A reciprocal comparison of these two groups showed that fractional urea excretion by the sheep with a high energy intake was significantly lower than in the group with a low energy intake. There were no differences in the glomerular filtration rate. A raised dietary energy intake in the presence of a low nitrogen intake caused marked natriuresis and kaliuresis. The results indicate that a raised dietary energy intake can be a significant factor in potentiating the renal effect of urea retention in sheep with a low nitrogen intake.     

The effects of two analogues of arginine-vasopressin (ornithine-vasopressin and desamino-D-arginine-vasopressin) on kidney function in sheep.

The effects of intravenous infusion of ornithine-vasopressin (OVP) and desamino-D-arginine-vasopressin (dDAVP) were studied in normal and hydrated Merino sheep. In normal sheep, OVP resulted in a diuresis, increased urinary sodium and potassium excretion, and a fall in the plasma potassium concentration. Renal plasma flow remained constant but glomerular filtration rate and filtration fraction rose markedly. dDAVP in normal sheep was antidiuretic, but its only significant effect was a small decrease in plasma osmolality. In the hydrated sheep OVP was antidiuretic and resulted in increased urinary excretion of sodium and potassium, and a fall in the plasma potassium level. Renal plasma flow fell, but glomerular filtration and filtration fraction tended to rise. dDAVP in the hydrated sheep was also antidiuretic but urinary sodium and potassium excretion was reduced. Renal plasma flow and glomerular filtration fell, with a small decrease in filtration fraction. These results suggest that the diuretic effect in normal sheep and the electrolyte-excreting effects in both normal and hydrated sheep of OVP are related to the increase in glomerular filtration, which in turn is dependent on the vasopressor activity of the hormone. The increase in glomerular filtration caused by OVP is due to an increase in the filtration fraction of an unchanged renal plasma flow, which could be brought about by an increase in renal efferent arteriolar tone. The effects of hydration of the sheep were the conventional increased urine flow, decreased urine osmolality and decreased solute-free water reabsorption. Sodium and potassium excretion rose slightly and plasma osmolality fell. Renal plasma flow and glomerular filtration both increased with little change in filtration fraction. These effects could be brought about by suppression of endogenous vasopressin and a decrease in both afferent and efferent renal arteriolar tone.     

Kidney retention of urea in sheep on a hypoprotein diet: study by retrograde perfusion of urea in the kidney pelvis

In order to study the role of the renal pelvis on urea sparing in sheep fed low protein diets, the pelvis was perfused through the ureter with 1M and 3M urea solutions. Eight ewes were used: four on a regular diet (total nitrogen 188.7 g.kg-1 dry matter) and the other four on a low protein diet (total nitrogen 109.4 g.kg-1 dry matter). On each animal, perfusions were performed on one kidney; the other one was kept as a control. Fractional excretion of urea (TEu) and urea (Cu), inulin, para-aminohippurate and osmolar clearances, were determined during five experimental periods of 30 min each (T = control, 1M = perfusion with 1M urea solution, R1 = first period of recovery, 3M = perfusion with 3M urea solution, R2 = second period of recovery). 1. During control periods sheep on low protein diet have a greater capacity of urea retention than sheep on regular diet, under antidiuretic conditions (inulin U/P = 200). The following data (means +/- S.D.) are all reduced in animals on low protein diet: TEu by 36% (0.38 +/- 0.19 vs. 0.59 +/- 0.28 for normal protein sheep, p less than 0.05), Cu by 55% (0.50 +/- 0.19 vs. 1.15 +/- 0.49 ml.min-1.kg-1 for normal sheep, p less than 0.01) and amount of urea excreted by 80% (2.1 +/- 0.7 vs. 10.4 +/- 2.7 mg.min-1 for normal sheep, p less than 0.01). 2. The linear regression analysis of the relationship between tubular reabsorption of urea and its filtered amount shows that the capacity of urea retention is significantly higher in low protein sheep and that the difference between the two groups is greater as the filtered amount increases. Following 1M and 3M perfusions, the capacity of urea reabsorption by the perfused kidneys is significantly decreased in low protein animals whereas there is no change in the normal ones. The result is that perfused kidneys of the low protein sheep increase the amount of urea excreted during these periods: urine concentration of urea (Uu) increases by 55% during R1 and by 144% during R2, TEu increases by 60% during R1 and by 147% during R2 and Cu increases by 40% during R1 and by 95% during R2, without any variation of urine flow rate. These changes could be understood, provided that an important transfer of the perfused urea to the renal medulla in the low protein sheep would reduce the concentration gradients which enhance urea passive reabsorption from the collecting ducts.(ABSTRACT TRUNCATED AT 250 WORDS)     

The renal response of sheep to a low dietary nitrogen intake

Renal functions were tested in sheep fed on a low nitrogen diet (LN sheep), with a daily N intake of 4.7 g (gross energy 17.76 . 10(6) J). Sheep given a high nitrogen diet (HN sheep) with 21.2 g N (24.12 . 10(6) J) acted as the control. The functions of the left kidney were measured in anaesthetized animals by the standard clearance technique. A comparison of HN and LN sheep showed that a low nitrogen intake led to a drop in the plasma urea level (from 5.91 +/- 0.35 to 2.87 +/- 0.36 mmol.1-1, (P less than 0.001), the glomerular filtration rate (GFR, from 36.6 +/- 3.6 to 20.7 +/- 2.4 ml.min-1, P less than 0.005), amount of urea excreted (from 106.7 +/- 18.1 to 15.7 +/- 3.3 mumol.min-1, P less than 0.001), fractional urea excretion (from 51.0 +/- 3.0 to 24.6 +/- 3.1 %, P less than 0.001) and the absolute tubular reabsorption of urea (Reaburea/GFR (from 3.06 +/- 0.27 to 2.12 +/- 0.28 mumol.ml-1, P less than 0.05), without a significant change in the effective renal plasma flow (182.6 +/- 20.0 and 138.5 +/- 21.0 ml.min-1, non-significant - N.S.) and in sodium and potassium excretory function. Free water clearance rose in LN sheep (from -0.53 +/- 0.11 to -0.19 +/- 0.06 ml.min-1, P less than 0.05) owing to inhibited urea excretion. A regression analysis of the relationship of the tubular reabsorption of urea to the amount of filtered urea (both normalized to the GFR) showed that the urea transport capacity of the tubules of LN sheep was significantly higher.(ABSTRACT TRUNCATED AT 250 WORDS)     

Branchial and renal handling of urea in the gulf toadfish,Opsanus beta: the effect of exogenous urea loading

The objective of this study was to determine whether the pulsatile facilitated diffusion transport mechanism (tUT) found in the gills of the gulf toadfish (Opsanus beta) and the active secretion transporter thought to be present in its kidney could be saturated when faced with elevated plasma urea concentrations. Toadfish were infused with four consecutive exogenous urea loads at a rate of 0, 150, 300 and 600 micromol kg(-1) h(-1). Initial plasma and urine urea concentrations were 8.1+/-0.9 and 12.4+/-1.5 mmol l(-1), respectively, and steadily increased with increasing infused loads of urea to a maximum of 36.8+/-2.8 mmol l(-1) in the plasma and 39.8+/-6.5 mmol l(-1) in the urine. There was only a very weak relationship (r=0.17) between pulse size (measured as branchial excretion during pulsatile excretion of urea) and plasma urea concentration (slope=9.79 micromol-N kg(-1) per mmol-N l(-1); P<0.05) suggesting that the branchial excretion mechanism was already saturated at normal plasma urea concentrations. Urine flow rate (0.15+/-0.03 ml kg(-1) h(-1)) and glomerular filtration rate (0.025+/-0.004 ml kg(-1) h(-1)) remained constant throughout the experiment despite the increased volume load. Renal urea secretion rate maintained a strong linear relationship (r=0.84) to plasma urea levels (slope=0.391 micromol-N kg(-1) h(-1) per mmol-N l(-1); P<0.001) with no observable transport maximum, suggesting that the renal secretory transport mechanism was not saturated even at plasma urea levels well above normal, in contrast to the branchial excretion mechanism.     

Levels of cellular retinol-binding proteins in the small intestine of rats during pregnancy and lactation

The movement and metabolism of vitamin A is dependent on a number of specific carrier proteins. The small intestine contains both cellular retinol-binding protein (type two) (CRBP(II], restricted to the villus-associated enterocytes, and cellular retinol-binding protein (CRBP), present primarily in supporting mesenchymal cells. The content of these proteins in the small intestine of prepartum and postpartum Sprague-Dawley rats was determined by radioimmunoassay. Levels of CRBP(II), but not CRBP, changed dramatically during this period. Total content of CRBP(II) in the small intestine rose precipitously in late pregnancy and continued to rise throughout lactation to a peak at day 21 postpartum more than 300% greater than in nulliparous, nonpregnant controls. In contrast, total small intestinal weight and CRBP content increased only approximately 100% from late pregnancy to day 21 of lactation. CRBP(II) concentration in the proximal and middle segments of small intestine (expressed on a g wet tissue, mg protein, or mg DNA basis) remained at control levels through day 17 of pregnancy, increased 50-100% in late pregnancy, then rose markedly at parturition to levels two- to threefold greater than controls. CRBP(II) concentration was then maintained at a relatively constant elevated level during the remainder of lactation, but decreased markedly after weaning, approaching control levels within 1 week. The concentrations of CRBP(II) in enterocytes isolated from the proximal two-thirds of the small intestine from rats on day 20 of pregnancy and days 1 and 16 of lactation, expressed on a mg DNA basis, were similar and approximately 60% greater than controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Early changes in renal function following chemically induced nephropathy

The functional changes in the rat kidney 24 h after administration of 2-bromoethanamine hydrobromide (BEA) have been extensively described. There is, however, little information regarding earlier alterations. The present study was designed to measure early changes in renal function in order to clarify further pathomechanisms of the BEA-induced lesion. Experiments were performed in two groups of Wistar rats with different infusion rates during the first 3 h following injection of 100 mg/kg BW BEA compared to sham-injected rats. Analysis included measuring urine flow, osmolality, urea, sodium and potassium as well as inulin and para-aminohippuric acid clearance. Our studies show a tubular as well as a glomerular involvement in BEA-induced nephropathy. A significantly higher urine flow occurred already in the first 30 min following injection of BEA. Urine osmolality began to decrease after 90 min, Na excretion was elevated at 3 h, K excretion was not significantly different from the control group, urea excretion was increased after 30 min. Contrary to other studies we found a continuously decreasing glomerular filtration rate and PAH clearance during the first 3 h. Our results suggest an early effect of BEA on tubular function (increasing sodium excretion), papillary concentration capacity (increasing urine flow combined with decreasing osmolality) and glomerular function (decreasing glomerular filtration rate).     

Renal excretion of urea in a small east African antelope, the dik-dik (Rhynchotragus kirkii)

1. A study on the renal handling of urea by the dik-dik antelope (Rhynchotragus kirkii) was conducted. 2. Plasma and urine samples were analysed for osmolality, urea and creatinine concentrations during dehydration and intra-ruminal loading of potassium and sodium solutions. 3. The glomerular filtration rate (GFR) of the dik-dik was found to be 182.6 +/- 11.7 ml/min/100 kg body mass. 4. Dehydration was observed to increase tubular urea reabsorption and increase plasma and urine osmolalities, but had no effect on the amount of urea filtered at the glomerulus. 5. Potassium loading increased both GFR and urine flow rate.     

Changes in maternal taurine levels in response to pregnancy and lactation

Taurine levels in various tissues and fluids of female rats were measured throughout pregnancy and lactation. The taurine concentration of liver markedly increased at days 19 and 21 of pregnancy to 188% of levels for nonpregnant, nonlactating control rats and then fell rapidly after delivery to reach only 30% of the control level by 3 days postpartum. Muscle and heart taurine concentrations were significantly negatively correlated with liver taurine levels. Brain taurine levels were low at days 14, 19 and 21 of pregnancy and day 14 of lactation. Urinary excretion of taurine decreased to 32% of control levels at day 21 of pregnancy and was negatively correlated with the hepatic taurine concentration over the course of pregnancy and lactation. The ratio of glycine- to taurine-conjugated bile acids was strongly negatively correlated with the hepatic taurine concentration. The milk taurine level was positively correlated with hepatic taurine concentration during lactation. The hepatic taurine pool appears to increase just before parturition and to rapidly decrease during the first few days of lactation when high levels of taurine are secreted in the milk. Our data suggests that the accumulation of taurine in the liver may be related to both a decreased renal clearance of taurine and a shifting of tauring from other tissues to the liver and that this enlarged pool of hepatic taurine may serve as a source of taurine for secretion in the early milk.     

Glucose metabolism in vivo in crossbred Holstein cattle feeding on different types of roughage during late pregnancy and early lactation

An experiment was carried out to study the glucose kinetics of crossbred Holstein cattle feeding on either hay or 5% urea treated rice straw during late pregnancy (21 days prepartum) and early lactation (30 days postpartum). In all 16 pregnant heifers (23–25 months of age) were selected for the experiments, including eight animals of two breed types, Holstein Friesian×Red Sindhi (50:50=50% HF) and Holstein Friesian×Red Sindhi (87.5:12.5=87.5% HF). They were divided into four groups of four animals each. Animals from the same breed type in each group were fed with either rice straw treated with 5% urea or pangola hay (Digitaria decumbens) as the source of roughage throughout the experiments. The glucose turnover rate in both types of crossbred Holstein cattle was determined using a continuous infusion of [U-¹⁴C] and 3-[³H]glucose during late pregnancy and early lactation. Total glucose entry and utilization rates increased significantly during lactation for all groups. Recycling of [C]glucose was, approximately, 20% in both crossbred cattle fed either hay or urea treated rice straw and was unaffected by the stage of late pregnancy or early lactation. Comparing 50 and 87.5% HF animals, arterial plasma glucose concentrations were slightly higher during pregnant periods but significantly higher in lactating periods in 50% HF animals. The ratio of specific radioactivity of arterial blood bicarbonate relative to that of arterial blood [¹⁴C]glucose in the lactating period, significantly decreased in 50% HF animals fed either urea treated rice straw or hay. An increase in udder blood flow during early lactation was significantly higher in 87.5% HF animals than in 50% HF animals. The uptake, arteriovenous differences and extraction ratio for glucose across the udder, significantly increased in the lactating period for all crossbred animals. Glucose uptake by the udder of 87.5% HF animals accounted for 65% of the total glucose turnover rate compared to a value of 46% in the lactating 50% HF animals. It can be concluded that both crossbred cattle fed either urea treated rice straw or hay exhibit the same body glucose turnover rate. The 87.5% HF animal has the genetic potential for a high milk yield and has high body and udder glucose metabolisms compared with 50% HF animals.     

Long-Term Responses to Loss of Renal Mass: Glomerular Changes: Compensatory Renal Hypertrophy in Dogs: Single Nephron Glomerular Filtration Rate

Kidney weight, length of superficial and juxtamedullary proximal tubules, glomerular diameter, kidney filtration rate and PAH clearance, sodium excretion and intrarenal distribution of filtration (with ¹⁴C-ferrocyanide) were measured in the remaining hypertrophic kidneys of dogs 10 days after unilateral nephrectomy. Whereas kidney weight increased to 75 percent of the original total renal mass, proximal tubule length and mean glomerular diameter remained unchanged. PAH and creatinine clearance, and absolute, but not fractional, sodium excretion, rose significantly. The ratio superficial/juxtamedullary filtration rate remained unchanged, indicating parallel increases of filtration in both cortical regions of hypertrophied kidneys.     

Renal responses to diuretics in the turtle

Summary We administered the diuretics furosemide and ethacrynic acid to conscious freshwater turtles to assess changes in renal function and plasma renin activity (PRA) in an animal which lacks a loop of Henle. Furosemide (2 and 5 mg/kg) produced no changes in blood pressure, hematocrit, plasma electrolytes, glomerular filtration rate (GFR), or PRA. Furosemide doubled urine volume while sodium excretion increased 20-fold and chloride and potassium excretion increased 12-fold (P<0.05 in each case). Net potassium secretion was observed. Ethacrynic acid (2 and 5 mg/kg) also produced no changes in blood pressure, hematocrit, plasma electrolytes, or PRA. At the lower dose GFR increased by 40% and urine volume nearly doubled (P<0.05 in each case). Sodium, chloride, and potassium excretion increased roughly 10-fold (P<0.05 in each case). At the higher dose, GFR increased by 80% and urine volume more than doubled (P<0.05 in each case). Sodium excretion rose 40-fold, chloride excretion rose 25-fold, and potassium excretion rose 10-fold (P<0.05 in each case). At both doses net potassium secretion occurred. The results demonstrate that both drugs inhibit tubular reabsorption in the turtle, acting primarily on distal segments of the nephron. The failure of either drug to alter PRA suggests that the turtle lacks a tubular mechanism for alterig renin release.Abbreviations GFR glomerular filtration rate - PRA plasma renin activity Supported by the University of Delaware Honors Program, American Heart Association of Delaware, NIH Biomedical Support Program, and USPHS #HL2808401     

Effects of atrial natriuretic factor on renal function and cyclic GMP production

Anesthetized beagle dogs received increasing doses of continuous infusions of a 26-amino-acid synthetic atrial natriuretic factor (ANF). Urinary sodium excretion rose in a dose-dependent manner to a maximum level similar to that seen after hydrochlorothiazide administration. Mean arterial blood pressure decreased, but only modestly, and not in a dose-dependent fashion. Dogs chronically retaining NaCl secondary to constriction of the thoracic inferior vena cava showed only modestly enhanced natriuresis when infused with similar levels of ANF. When ANF was infused directly into the renal artery of anesthetized beagles, a dose-dependent natriuresis and calciuresis were observed with maximal fractional sodium excretion averaging approximately 8%. Although glomerular filtration tended to increase, the average dose-related changes were not significant. Cyclic GMP excretion was increased during intra-renal-arterial infusion of ANF. Excretion of cyclic GMP by both the infused and noninfused kidneys was equal, which suggests that urinary cyclic GMP was not nephrogenous but derived from the elevated circulating levels. These and other data from rats dissociate changes in urinary cyclic GMP excretion and sodium excretion.     

Abnormal Glomerular Filtration Rate,Renal Plasma Flow,and Renal Protein Excretion in Recent and Short-term Diabetics

Glomerular filtration rate and renal plasma flow were simultaneously determined in comparable groups of 43 diabetics less than 40 years of age and with a duration of diabetes less than 10 years and 32 control subjects. The average glomerular filtration rate in the diabetic group was significantly higher than that in the control group (P <0·01). The average renal plasma flow in the diabetic group was found to be significantly lower than that in the control group (P <0·05). The filtration fraction in both male and female diabetics was significantly higher than in the male and female control groups (P <0·001). These changes were found to be present even in recent juvenile diabetics with disease of a duration of less than one year. No correlation was apparent between the average levels of serum growth hormone and glomerular filtration rate.The urinary protein excretion was determined in 36 diabetic and 38 healthy subjects comparable with regard to glomerular filtration rate. In the diabetic group there was a greater frequency of cases with higher protein excretion rates (P <0·02). The average protein excretion rate was increased even in diabetics with less than one year''s duration of the disease.The results of the changes in renal haemodynamics in subjects with recent and short-term diabetes are compatible with the presence of a constrictive state of the vas efferens leading to an increase in the filtration pressure. The increase in protein excretion rate may similarly be a consequence of this process or of an increase in the glomerular permeability with augmented molecular sieving of proteins or both.     

Urinary excretion of cGMP in response to atrial natriuretic peptide in dogs with acute pancreatitis

Previous studies have shown that when atrial natriuretic peptide (ANF) is given to anaesthetized dogs with hypovolemic acute pancreatitis, it will produce a diuresis and natriuresis but will not elevate the glomerular filtration rate (GFR). When the same dose of peptide is given to dogs equally hypovolemic (hemorrhage) but without pancreatitis, a brisk increment in GFR occurs. GFR will, however, rise in dogs with pancreatitis in response to other peptides, such as glucagon. In these studies we assessed cGMP excretion as a marker for ANF effect in both normal anaesthetized dogs and dogs with acute experimental pancreatitis. In each group, urinary output and sodium excretion increased significantly, but GFR rose only in the control group. Urinary excretion of cGMP rose equally and dramatically in both control and experimental animals. We conclude that GFR is prevented from rising in dogs with experimental pancreatitis following ANF, but this effect does not depend on depressed cGMP generation.     

The actions of cortisol on fetal renal function

Renal function was studied in 6 fetal sheep, aged 126-135 days, before and after 3 injection of 15 mg of cortisol given at intervals of 12 h. Cortisol caused a significant rise in both renal blood flow (P less than 0.05) and glomerular filtration rate (P less than 0.005), and in urine flow rate (P less than 0.02) but it did not consistently cause a natriuresis. The urinary pH was unchanged following cortisol treatment, but bicarbonate excretion increased. Urinary phosphate excretion was increased (P less than 0.005) because of a rise in filtered phosphate and a fall in phosphate reabsorption. The titratable acid excretion increased (P less than 0.005) but urinary ammonium excretion did not. The total amount of sodium reabsorbed increased after cortisol but the amount of sodium reabsorbed in the proximal tubule did not increase, so fractional reabsorption in the proximal tubule decreased from 61.7 +/- 4.1% to 47.3 +/- 4.2% (P = 0.01). The total amount of sodium reabsorbed in the distal tubule increased and distal fractional reabsorption increased from 33.3 +/- 2.4% to 47.3 +/- 4.2% (P less than 0.01). Cortisol may increase the capacity of the immature kidney to play a role in fluid and electrolyte homeostasis by increasing glomerular filtration rate and delivering more sodium and water to the distal nephron where the reabsorption of sodium and water can be modified independently and in accordance with need.     

Serum hippurate and its excretion in conservatively treated and dialysed patients with chronic renal failure.

54 healthy volunteers or patients with normal kidney and liver function, 17 patients with decreased kidney function and 12 dialysed patients were evaluated for their serum hippurate accumulation and kidney excretion. It was found that there was an inverse relationship between serum hippurate and the clearance of endogenous creatinine (CCr) and a free relationship between fractional excretion of hippurate and CCr. The excretory capacity in residual nephrons was increased. This was caused by the greater glomerular filtration load which increased up to 25 times and tubular secretion which increased 7 times in dialysed patients. The relative contribution of glomerular filtration to hippurate excretion rose from about 20% in controls to almost 50% in dialysed patients. True kidney adaptation was localized in the organic anion transport system of proximal tubules.     

Effects of intra-peritoneal injection with NH4Cl, urea, or NH4Cl+urea on nitrogen excretion and metabolism in the African lungfish Protopterus dolloi

This study aimed to (1) determine if ammonia (as NH(4)Cl) injected intra-peritoneally into the ureogenic slender African lungfish, Protopterus dolloi, was excreted directly rather than being converted to urea; (2) examine if injected urea was retained in this lungfish, leading to decreases in liver arginine and brain tryptophan levels, as observed during aestivation on land; and (3) elucidate if increase in internal ammonia level would affect urea excretion, when ammonia and urea are injected simultaneously into the fish. Despite being ureogenic, P. dolloi rapidly excreted the excess ammonia as ammonia within the subsequent 12 h after NH(4)Cl was injected into its peritoneal cavity. Injected ammonia was not detoxified into urea through the ornithine-urea cycle, probably because it is energetically intensive to synthesize urea and because food was withheld before and during the experiment. In addition, injected ammonia was likely to stay in extracellular compartments available for direct excretion. At hour 24, only a small amount of ammonia accumulated in the muscle of these fish. In contrast, when urea was injected intra-peritoneally into P. dolloi, only a small percentage (34%) of it was excreted during the subsequent 24-h period. A significant increase in the rate of urea excretion was observed only after 16 h. At hour 24, significant quantities of urea were retained in various tissues of P. dolloi. Injection with urea led to an apparent reduction in endogenous ammonia production, a significant decrease in the hepatic arginine content, and a significantly lower level of brain tryptophan in this lungfish. All three phenomena had been observed previously in aestivating P. dolloi. Hence, it is logical to deduce that urea synthesis and accumulation could be one of the essential factors in initiating and perpetuating aestivation in this lungfish. Through the injection of NH(4)Cl + urea, it was demonstrated that an increase in urea excretion occurred in P. dolloi within the first 12 h post-injection, which was much earlier than that of fish injected with urea alone. These results suggest that urea excretion in P. dolloi is likely to be regulated by the level of internal ammonia in its body.     

A study of some serum mineral levels before and during pregnancy and during lactation period of sheep and cattle

The purpose of this study was to determine serum Cu, Zn, Mn, K, and Mg levels before and during pregnancy and during the lactation period of sheep and cattle and to determine the relationships between periods. For this purpose, blood samples of 14 healthy, pregnant Brown Swiss cows fed under normal condition and 36 Karakaş (İvesi × Akkaraman) sheep were used. Blood samples were analyzed using an atomic absorption spectrophotometer. There were significant differences between before pregnancy and during pregnancy, and during pregnancy and the lactation period for serum Zn concentration; also before pregnancy and during pregnancy, and before pregnancy and the lactation period for serum K concentration in cows (p<0.05). There were significant differences between before pregnancy and the lactation period for serum Cu concentration, and before pregnancy and during pregnancy for serum K concentration; also pregnancy and the lactation period for serum Mg concentration in sheep (p<0.05).