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PubMed2002

Neurohypophysial hormones and renal function in fish and mammals.

The two major basic neurohypophysial peptides, arginine vasopressin (AVP) of mammals and arginine vasotocin (AVT) of all non-mammalian vertebrates, share common structure and major roles in regulating renal function. In this review the complexity of AVP actions within the mammalian kidney is discussed and comparisons are made with the emerging picture of AVT's renal effects in fish. It has become apparent that the antidiuretic action of the neurohypophysial hormones is an ancient phylogenetic phenomenon, although this is based upon reduced glomerular filtration in fish by comparison with predominant tubular effects in mammals. Nonetheless, there appears to be retention of AVP effects upon the functional heterogeneity of nephron populations in mammals. Preliminary evidence for the possible existence of V(2)-type (tubular) neurohypophysial hormone receptors in fish, implies possible AVT actions which parallel those in mammals on tubular ion transport. Further insight from recent mammalian tubule microperfusion studies suggests that in teleost fish both apical (tubular lumen) and basolateral (blood borne) AVT have the potential to modulate renal function, though this remains to be examined.

Amino Acid Sequence↗

PubMed1994

Enhanced selectivity of oxytocin antagonists containing sarcosine in position 7.

Neurohypophyseal hormone analogues containing sarcosine (Sar) in position 7 were prepared to design more potent and selective oxytocin antagonists. The three analogues (1-3) of [Sar7]arginine-vasopressin ([Sar7]AVP) and six analogues (4-9) of [Sar7]arginine-vasotocin ([Sar7]AVT) had a reduced affinity for antidiuretic V2 receptors. The [Sar7]AVP derivatives (1-3) were potent antiuterotonic (in vitro pA2 = 7.5-8.4, in vivo 6.6-7.1) and antipressor (pA2 = 7.2-8.0) agents. The [Sar7]AVT analogues (4-9) were more potent and selective uterotonic antagonists (in vitro pA2 = 7.9-8.6, in vivo 7.1-7.5); their antipressor potencies were reduced (pA2 = 6.4-7.7). The change of the antagonistic potencies was paralleled by a change in the receptor affinities. Among other antiuterotonic analogues, [Mca1, D-Phe2, Sar7]AVT (4, Mca = beta-mercapto- beta,beta-cyclopentamethyl-enepropionic acid) and [Mca1, D-Tyr(OEt)2,Sar7]AVT (6) were synthesized, two highly potent antiuterotonic compounds (in vitro pA2 = 8.3, in vivo 7.4 and 7.5, respectively) with reduced antipressor activity (pA2 = 6.4) and reduced binding affinity to V2 receptors (Kd = 421 and 35 nM, respectively) and no anti-antidiuretic effect. Another potent antiuterotonic analogue, [Mca1,D-Trp2,-Sar7]AVT (9, in vitro pA2 = 7.9, in vivo 7.5) has virtually no binding capability to V2 receptors (Kd approximately 0.3 mM). These analogues should lead to the design of even more potent and selective oxytocin antagonists.

Amino Acid Sequence↗

PubMed1989

Solid-phase synthesis of 16 potent (selective and nonselective) in vivo antagonists of oxytocin.

We describe the synthesis and some pharmacological properties of 16 new in vivo antagonists of oxytocin. These are based on modifications of three peptides: A, B, and C. A is our previously reported potent and selective antagonist of the vasopressor (V1 receptor) responses to arginine-vasopressin (AVP)/weak oxytocin antagonist, [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid), 2-O-methyltyrosine]arginine-vasopressin (d(CH2)5[Tyr(Me)2]AVP. B reported here, the Ile3 analogue of A, is d(CH2)5[Tyr(Me)2]AVT (5 below) and C is our previously reported potent nonselective oxytocin antagonist/AVP V1 antagonist, [1-(beta-mercapto-beta,beta-pentamethylenepropionic acid),2-O- methyltyrosine,8-ornithine]vasotocin (d(CH2)5[Tyr(Me)2]OVT). The following substitutions and deletions, alone or in combination, were employed in A, B, and C: 1-deaminopenicillamine (dP); D-Tyr(Alk)2 (where Alk = Me or Et), D-Phe2; Val4, Thr4; delta 3-Pro7; Lys8, Cit8; desGly9, desGly-NH2(9), Ala-NH2(9); Leu-NH2(9); Arg-NH2(9). The 16 new analogues are (1) d(CH2)5[D-Tyr(Me)2]AVP, (2) d(CH2)5[D-Tyr(Me)2, Val4,delta 3-Pro7]AVP, (3) d(CH2)5[D-Tyr-(Et)2, Val4,Lys8]VP, (4) d(CH2)5[D-Tyr(Et)2,Val4,Cit8]VP, (5) d(CH2)5[Tyr(Me)2]AVT, (6) d(CH2)5[Tyr(Me)2,Lys8]VT, (7) dP[Tyr(Me)2]AVT, (8) dP[Tyr(Me)2,Val4]AVT, (9) d(CH2)5[D-Tyr(Me)2, Val4]AVT, (10) d(CH2)5[D-Phe2,Val4]AVT, (11) d(CH2)5[Tyr(Me)2,Thr4]OVT, (12) d(CH2)5[Tyr(Me)2,Thr4,Ala-NH2(9)]OVT, (13) d(CH2)5[Tyr(Me)2,Thr4,Leu-NH2(9)]OVT, (14) d(CH2)5[Tyr(Me)2,Thr4,Arg-NH2(9)]OVT, (15) desGly-NH2(9),d(CH2)5[Tyr(Me)2,Thr4]OVT, (16) desGly9,d(CH2)5[Tyr(Me)2,Thr4]OVT. 1-4 are analogues of A, 5-10 are analogues of B, and 11-16 are analogues of C. Their protected precursors were synthesized either entirely by the solid-phase method or by a combination of solid-phase and solution methods (1 + 8 or 8 + 1 couplings). All analogues were tested in rats for agonistic and antagonistic activities in oxytocic (in vitro, without and with Mg2+, and in vivo) assays as well as by antidiuretic and vasopressor assays. All analogues exhibit potent oxytocic antagonism in vitro and in vivo. With an in vitro pA2 (in the absence of Mg2+) = 9.12 +/- 0.09, dP[Tyr(Me)2]AVT is (7) one of the most potent in vitro oxytocin antagonists reported to date. Fifteen of these analogues (all but 6) appear as potent or more potent in vivo oxytocin antagonists than C (pA2 = 7.37 +/- 0.17). Analogues 1-9 and 14 are potent AVP V1 antagonists. Their anti-V1 pA2 values range from 7.92 to 8.45. They are thus nonselective oxytocin antagonists.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1997

Potentiation by vasopressin of adrenergic vasoconstriction in the rat isolated mesenteric artery.

1. The aim of the present study was to investigate in rat mesenteric artery rings whether low concentrations of vasopressin could modify the contractile responses to noradrenaline and electrical stimulation of perivascular nerves. 2. Vasopressin (10[10]-10[-7] M) caused concentration-dependent contractions (pD2 = 8.36+/-0.09). The V1-receptor antagonist d(CH2)5Tyr(Me)AVP (10[-9]-10[-8] M) produced parallel rightward shifts of the control curve for vasopressin. Schild analysis yielded a pA2 value of 9.83 with a slope of 1.10+/-0.14. 3. Vasopressin (3 x 10[-10] and 10[-9] M) caused concentration-dependent potentiation of the contractions elicited by electrical stimulation (2-8 Hz; 0.2 ms duration for 30 s) and produced leftward shifts of the concentration-response curve for noradrenaline. The V1-receptor antagonist induced concentration-dependent inhibitions of potentiation induced by vasopressin. The selective V1-receptor agonist [Phe2, Orn8]-vasotocin (3 x 10[10] and 10[-9] M) induced potentiation of electrical stimulation-evoked responses which was also inhibited in the presence of the V1 antagonist (10[-8] M). In contrast, the V2-receptor agonist deamino-8-D-arginine vasopressin (desmopressin 10[-8]-10[-7] M) did not modify the electrical stimulation-induced responses and the V2-receptor antagonist [d(CH2)5, D-Ile2, Ile4, Arg8]-vasopressin (10[-8]-10[-7] M) did not affect the potentiation evoked by vasopressin. 4. In artery rings contracted by 10(-6) M noradrenaline in the presence of 10(-6) M guanethidine and 10(-6) M atropine, electrical stimulation (2, 4 and 8 Hz) produced frequency-dependent relaxations which were unaffected by 10(-9) M vasopressin but abolished by 10(-6) M tetrodotoxin. 5. Vasopressin also potentiated contractions elicited by KCl and contractions induced by addition of CaCl2 to KCl depolarized vessels. The augmenting effects were inhibited by the V1 antagonist. 6. In the presence of the calcium antagonist nifedipine (10[-6] M), vasopressin failed to enhance the contractile responses to electrical stimulation, noradrenaline and KCl. 7. The results demonstrate that low concentrations of vasopressin strongly potentiate the contractions to adrenergic stimulation and KCl depolarization. This effect appears to be mediated by V1 receptor stimulation which brings about an increase in calcium entry through dihydropyridine-sensitive calcium channels.

Animals↗

PubMed1968

Interaction of polypeptide hormones with lipid monolayers.

1. The interaction between lipid monolayers spread on the surface of water and oxytocin, [8-arginine]-vasotocin and [1-asparagine-5-valine]-angiotensin II in the subphase was investigated in a Langmuir surface trough by studying the changes in pressure produced on injection of various quantities of the polypeptide solution under the film. 2. The effect of 2m- and 4m-urea on the character of the adsorption is reported. 3. Structures for the adsorbed films formed in this way are suggested. 4. If the lipid monolayer is taken as a suitable model of cell membranes, then it may be supposed that the effect of such structures forming in cell membranes would be to provide effective ;pores' to facilitate the movement of water and other small molecules across the membrane.

Adsorption↗

PubMed1984

The stimulation of Na+, K+-ATPase activity in the medulla of the rat kidney by [arginine] vasopressin and its analogues.

Total and Na+, K+-ATPase activities have been measured in sections (10 micron thick) from blocks of rat kidney cultured for 5 h at 37 degrees C, pH 7.5, in Glasgow Eagle's Minimum Essential Medium. Synthetic [arginine]vasopressin [( Arg]VP) stimulated ATPase activity in the thick tubular cells of the renal outer medulla over the concentration range 0.01-10 fmol/l, but failed to affect ATPase activity in the proximal and distal convoluted tubules of the cortex. The increase in medullary total ATPase activity induced by [Arg]VP and its analogues was wholly due to stimulation of Na+, K+-ATPase activity. Stimulation of medullary ATPase activity was blocked by [Arg]VP antiserum. The [Arg]VP analogues desmopressin, [lysine]vasopressin, [arginine]vasotocin and oxytocin stimulated medullary Na+, K+-ATPase activity, the three last-named analogues being considerably less potent than [Arg]VP.

Animals↗

PubMed1996

Prostaglandin E2 inhibits antidiuretic hormone induced transepithelial sodium transport and cAMP production in frog skin epithelium (Rana esculenta).

The stimulation of transepithelial sodium transport by arginine vasotocin (AVT) and the ability of prostaglandin E2 (PGE2) to inhibit the AVT dependent sodium transport was examined on pieces of frog skin taken from different regions of the frog. The basal sodium transport was of the same magnitude in the abdominal, thoracal and upper and lower dorsal region. In all regions the sodium transport could be stimulated by AVT, though the stimulation was highest in the abdomen. Subsequent addition of PGE2 caused a significant inhibition of the AVT dependent sodium transport in the abdomen but had only minor effects on the other parts of the skin. Therefore, pieces of skin from the abdomen were selected for the remaining experiments. Addition of PGE2 to skin pieces in the presence of AVT resulted in a hyperpolarization of the cellular potential and a decrease in the transepithelial sodium transport, indicating a decreased apical sodium permeability. This was correlated with a decrease in cellular cAMP contents. We conclude that frog skin exhibits large regional differences in sensitivity to AVT and that PGE2 only modulates the natriferic effect of AVT in the abdomen.

Animals↗

PubMed1997

Mesotocin gene expression in the diencephalon of domestic fowl: cloning and sequencing of the MT cDNA and distribution of MT gene expressing neurons in the chicken hypothalamus.

This study focuses on the structure and expression of the mesotocin (MT) gene in the chicken hypothalamus. Using an anchored and nested RT-PCR strategy, combined with circular RACE-PCR, the full length sequence of the chicken MT cDNA was obtained. The cDNA and derived amino acid sequences conformed to the structure of the oxytocin-like gene family. However, unlike most mammalian species, there does not appear to be frequent gene conversion between the MT and AVT cDNA sequences. A single specific hybridization signal of 1.2 kb was detected by Southern analysis of chicken genomic DNA, indicating only a single gene copy in the chicken genome. Northern analysis of hypothalamic RNA revealed a single band at approximately 0.6 kb. Using the same probe for in situ hybridization histochemistry, MT-mRNA was demonstrated to be predominantly localized in the parvocellular, magnocellular and periventricular subgroups of the paraventricular nucleus and, when compared to the distribution of neurons containing arginine-vasotocin (AVT)-mRNA in the same region, with far fewer neurons expressing the MT gene in the lateral subgroups. Only few and scattered neurons expressing the MT gene were found in the ventral and external subgroups of the supraoptic nucleus in which many neurons contain AVT transcripts, as demonstrated in consecutive sections. In all nuclei investigated, the intensity of AVT and MT hybridization signals per cell was approximately equal. No specific labelling for MT-mRNA was found in the bed nucleus of the stria terminalis, nor the nucleus accumbens. Using immunocytochemical detection of AVT and in situ hybridization for neurons expressing MT-mRNA, some neurons were found to contain both AVT and MT gene products in the paraventricular nucleus but not in the supraoptic nucleus.

Amino Acid Sequence↗

PubMed1976

Studies in vivo on the effects of parathyroid hormone upon kidney cyclic adenosine 3',5'-monophosphate content using rapid tissue fixation by microwave irradiation.

Microwave irradiation is shown to be a useful method for simultaneously killing chicks and fixing tissues. Renal adenylate cyclase and phosphodiesterase activities were rapidly abolished by microwaving. The increase in chick kidney cyclic adenosine 3',5'-monophosphate (cyclic AMP) content produced by intravenous bovine parathyroid hormone (PTH) injection was much greater in microwaved birds than in those killed by cervical dislocation with subsequent tissue fixation in liquid nitrogen. After PTH injection there was a prolonged elevation of renal cyclic AMP content. At the time of maximum response (2 minutes), log. dose-response curves were linear in the dose range 0.1-10 U. The responses to three different bovine PTH preparations were indistinguishable. Arginine vasopressin, arginine vasotocin, salmon calcitonin and prostaglandin E1 did not affect kidney cyclic AMP content within 2 minutes. Because of its specificity and precision, the method is of use for the in vivo bioassay of PTH. Injection of CaCl2 (20 mumoles) 1 minute before, or conjointly with, bovine PTH inhibited the subsequent increase in kidney cyclic AMP content. The synthetic bovine PTH peptide fragments BPTH (1-34) and BPTH (2-34) both increased chick kidney cyclic AMP content. The use of such fragments allows investigation of the structural requirements of PTH for interaction with the systems regulating cyclic AMP metabolism in the kidney in vivo.

Animals↗

PubMed2006

Valence-sensitive neurons exhibit divergent functional profiles in gregarious and asocial species.

The medial bed nucleus of the stria terminalis (BSTm) influences both social approach and social aversion, suggesting that this structure may play an important role in generating motivational and behavioral differences between gregarious and asocial species. However, no specific neurons have been identified within the BSTm that influence species-typical levels of sociality or that mediate approach and avoidance. Using five songbird species that differ selectively in their species-typical group sizes, we now demonstrate that vasotocin-immunoreactive (VT-ir) neurons of the BSTm exhibit very different immediate early gene responses to same-sex stimuli in gregarious and asocial species. Exposure to a same-sex conspecific increases VT-Fos colocalization in gregarious species while decreasing colocalization in relatively asocial species. We additionally demonstrate that these neurons are selectively activated by social stimuli that normally elicit affiliation (positively valenced social stimuli) but not by stimuli that elicit aversion (negatively valenced social stimuli). Constitutive Fos activity of the VT-ir neurons is also significantly greater in the gregarious species, and the two most social species express significantly more VT-ir neurons. These findings demonstrate that the properties of valence-sensitive neurons evolve in relation to sociality and indicate that gregarious species accentuate positive stimulus properties during social interactions.

Animals↗

PubMed1996

Separate agonist and peptide antagonist binding sites of the oxytocin receptor defined by their transfer into the V2 vasopressin receptor.

The neurohypophyseal nonapeptide oxytocin (OT) is the main hormone responsible for the initiation of labor; uterus contraction can be enhanced by application of oxytocin or suppressed by oxytocin antagonists. By transfer of domains from the G protein-coupled OT receptor into the related V2 vasopressin receptor, chimeric "gain in function" V2/OT receptors were produced that were able to bind either OT receptor agonists or a competitive peptide antagonist with high affinity. The binding site for the OT antagonist d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr9]vasotocin was found to be formed by transmembrane helices 1, 2, and 7 with a major contribution to binding affinity by the upper part of helix 7. These transmembrane receptor regions could be excluded from participating in OT binding. For agonist binding and selectivity the first three extracellular receptor domains were most important. The interaction of the N-terminal domain and of the first extracellular loop of the OT receptor with the linear C-terminal tripeptidic part of oxytocin was demonstrated. Furthermore, the second extracellular loop of the OT receptor could be identified to interact with the cyclic hormone part. These three domains contribute to OT binding by synergistic interaction with oxytocin but not with the competitive antagonist. Our results provide evidence for the existence of separate domains and different conformations of a peptide hormone receptor involved in binding and selectivity for agonists and peptide antagonists.

Affinity Labels↗

PubMed1992

Alterations in uterine contractility during the oviposition cycle in domestic hens.

1. The potencies of several neurohypophysial hormones were examined at different times during the oviposition cycle in an in vitro fowl oxytocic assay. 2. Uterine tissues were removed 2 h before (-2h-OP), immediately after (0h-OP) and 5 h after (+5h-OP) spontaneous oviposition. In addition, uterine tissue was removed immediately after oviposition was induced, by administering prostaglandin E2 2 h before an expected oviposition (Induced-OP). 3. The rank order of oxytocic potencies for the peptides was arginine vasotocin = vasopressin greater than oxytocin greater than mesotocin. The sensitivity of the uterus to the hormones was 0h-OP = Induced-OP greater than -2h-OP = +5-OP. 4. These results suggest that uterine sensitivity to neurohypophysial hormones changes during the oviposition cycle in domestic fowls.

Animals↗

PubMed1972

Osmotic regulation of toad bladder responsiveness to neurohypophyseal hormones.

The effect of dilution of the interstitial fluids on the responsiveness of the toad urinary bladder to antidiuretic hormones has been examined in vivo and in vitro. Toads were given periodic injections with vasopressin while in water so that their plasma osmolality fell below 190 mosmoles/kg H(2)O. The hydraulic conductivity of bladders which had been removed from the animal and fixed with 1% glutaraldehyde was 10-fold less in overhydrated toads than in normally hydrated controls. A similar inhibitory phenomenon was observed in in vitro studies, when the tonicity of Ringer's fluid in which the bladders were suspended was lowered from its isotonic value. Mannitol, but not urea, could be effectively substituted for one-half of the NaCl content of Ringer's fluid. In other experiments it has been shown that the responsiveness of the bladder to vasotocin is depressed during bulk water movement across the tissue. This "flux inhibition" was found to depend upon the velocity and the duration of water flow from mucosa to the serosa. It is suggested that the responsiveness of the toad bladder to antidiuretic hormones diminishes as the effective osmotic pressure of the interstitial fluids declines.

Animals↗

PubMedDate not supplied

The role of pulmocutaneous baroreceptors in the control of lymphatic heart rate in the toad Bufo marinus.

The influence of increased pulmocutaneous arterial systolic pressure on amphibian lymph heart activity was determined in Bufo marinus. Arginine vasotocin-induced increases in systolic arterial pressure of greater than 0.5 kPa significantly (P<0.0002) decreased lymph heart rate. Denervation of the recurrent laryngeal nerve led to an increase in arterial pressure of 3.88 kPa in test animals compared to control animals. Denervation abolished lymph heart response to increased arterial pressure for an average of 38 min. Direct stimulation to the recurrent laryngeal nerve stopped lymph heart activity without an increase in arterial pressure. These data indicate that baroreceptors in the pulmocutaneous artery can decrease lymph heart rate during periods of either direct stimulation or elevated arterial pressure. The data also support lymph hearts as effectors for aortic and carotid baroreceptors.

Animals↗

PubMedDate not supplied

Renal response to dietary protein in the house sparrow Passer domesticus.

Many birds switch seasonally or during ontogeny between diets of varying protein content. In mammals, high-protein diets induce hypertrophy of the kidney in general and of the thick ascending limbs (TAL) in particular, along with increases in glomerular filtration rate (GFR) and urine flow. A hypothesis to explain these phenomena is that the TAL become increasingly sensitive to peptide hormones (glucagon and antidiuretic hormone [ADH]) released in response to protein feeding; the consequent enhancement of ion reabsorption dilutes urine reaching the macula densa, thereby suppressing tubulo-glomerular feedback (TGF) and causing a rise in GFR. Avian kidneys possess most of the elements involved in this mechanism, including loops of Henle with TAL, sensitivity of TAL to ADH (arginine vasotocin [AVT] in birds), and the elements of TGF. We therefore hypothesized that switching from a low-protein to a high-protein diet would induce responses in birds similar to those found in mammals. We tested this hypothesis by feeding house sparrows, Passer domesticus, isocaloric diets containing either 8% or 30% protein. Birds on high-protein food had larger renal medullae, both in mass and in TAL diameter, but no increase in whole-kidney mass. Urine flow was approximately doubled on high-protein food, but there was no change in GFR. We were not able to detect an increased sensitivity of AVT-induced adenylyl cyclase activity in TAL from high-protein animals, and responsiveness to glucagon was higher in TAL from birds eating low-protein food. We are unable to conclude that a suppression of TGF is responsible for the rise in urine flow in birds eating high-protein foods, and the mechanisms behind the medullary hypertrophy and the diuresis remain to be fully explored.

Animals↗

PubMedDate not supplied

Water potential receptors in the skin regulate blood perfusion in the ventral pelvic patch of toads.

Blood cell flux (BCF) in ventral pelvic skin capillaries was measured in conscious unrestrained Bufo bufo, using a laser Doppler flowcytometer. Hydrated toads responded to water contact with a small but significant increase in BCF. Dehydration alone did not change the BCF in seat patch skin before water contact. However, water contact by dehydrated toads elicited a rapid 600% increase in BCF. The BCF and water uptake of dehydrated toads rehydrating in water declined over 2 h but remained significantly above the low, constant values measured in hydrated toads. Arginine vasotocin injection in hydrated toads did not change skin BCF, but water uptake increased, and urine production decreased. Injection of the beta -adrenergic agonist isoproterenol increased BCF in hydrated toads by 900% and also increased the rate of water uptake. These increases corresponded in magnitude and duration to the response to water contact observed in dehydrated toads. Injection of dehydrated toads with the beta -adrenergic antagonist propranolol significantly reduced both BCF and water uptake. These results are consistent with an autonomic reflex mediated by skin water potential receptors that regulate blood perfusion of ventral pelvic skin.

Adrenergic beta-Agonists↗

PubMedDate not supplied

General function and endocrine control of the posterior lymph hearts in Bufo marinus and Rana catesbeiana.

The effects of hypervolemia and graded increases in arginine vasotocin (AVT), angiotensin II (ANGII), and atrial natriuretic peptide (ANP) on lymph heart pressure (P(lh)) and rate (f(lh)) were examined in Bufo marinus and Rana catesbeiana. The P(lh) and f(lh) for normally hydrated B. marinus at rest were 1.45+/-0.01 kPa and 52.8+/-0.38 beats min(-1). The P(lh) and f(lh) were significantly lower in R. catesbeiana, 1.05+/-0.01 kPa and 48.4+/-0.35 beats min(-1). Hypervolemia, induced by intravenous infusion of isotonic saline, stopped the lymph hearts at volumes of 0.48%+/-0.06% and 0.32%+/-0.04% body mass in B. marinus and R. catesbeiana, respectively, equivalent to an 8% increase of their respective plasma volumes. ANP had no effect on P(lh) or f(lh) at any of the dosages tested. ANGII decreased f(lh) in both species, approximating the physiological range of concentrations. AVT, at physiological concentrations, increased P(lh) 48% in B. marinus and 38% in R. catesbeiana without changing f(lh) in either species. At higher than physiological dosages, P(lh) and f(lh) in both species declined. The results suggest that AVT, normally released during hemorrhage and dehydration, would increase lymph heart output and help compensate for the hypovolemia. This is a contrary result to previous work using supraphysiologic doses of AVT.

Analysis of Variance↗

PubMedDate not supplied

Osmotically absorbed water preferentially enters the cutaneous capillaries of the pelvic patch in the toad Bufo marinus.

Cutaneously absorbed water in anurans has two potential routes of movement from the skin interstitium into the body fluids, via the cutaneous capillaries and/or the lymphatic system. We investigated the lymphatic route at the pelvic patch skin under the influence of isoproterenol and arginine vasotocin in Bufo marinus by continuously aspirating lymph from the lymph sacs draining the pelvic patch while the animals absorbed water. Changes in body mass, lymph mass, and lymph osmolality were measured. If absorbed water entered the lymph space directly, we expected, relative to controls, (1) no difference in change in body mass, (2) lymph mass to be greater, and (3) lymph osmolality to be lower. None of these predictions were confirmed. We also tested the possibility that absorbed water was stored in the skin interstitium by measuring the surface density of pelvic skin immediately after it absorbed water. If water was stored, we expected the surface density of this skin to be greater than that of control skin. No difference in surface density was found. These results provide strong evidence that absorbed water does not directly enter the lymphatic system and is not stored in the skin. Consequently, osmotically absorbed water must enter via a transcapillary route.

Animals↗