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At least 235 records · Page 13Linked to original sources
PubMed1983

Role of progesterone on oocyte maturation in the egg-brooding hylid frog Gastrotheca riobambae (Fowler).

In the egg-brooding frog Gastrotheca riobambae (Fowler), oocyte maturation is comparable to the situation of other frog species. In isolated follicles, progesterone induces only germinal vesicle breakdown (GVBD), while human chorionic gonadotropin (hCG) induces GVBD and ovulation. In addition, defolliculated oocytes respond with GVBD to the treatment with progesterone, while hCG has no effect. As in other frogs, oocyte maturation in vitro depends on hormonal action and on the presence of divalent cations. In this frog, progesterone or a similar hormone conditions the brooding pouch for reproduction and induces pouch closure. Follicles from frogs with closed pouches showed GVBD after 15-17 hours of incubation with progesterone, while those from frogs with open pouches took 19-24 hours for GVBD. These findings suggest that follicles become stimulated for maturation when the pouch is closed and that this stimulated condition is maintained for several weeks in advance of the process of oocyte maturation. In G. riobambae, the external appearance of the pouch aperture indicates the reproductive condition of the ovary.

Animals↗
PubMed1989

Seasonal variation in freeze tolerance and ice content of the tree frog Hyla versicolor.

Freeze tolerance and ice content of Hyla versicolor showed pronounced variation between summer (June) and winter (December). Summer frogs survived freezing at -3 degrees C for up to 9 hr and ice accumulation up to 50% of their total body water. A time course of ice formation indicated that an equilibrium level was reached in approximately 15 hr. Thus, the lethal ice content was less than the equilibrium ice content for these conditions (63.1%). A second group was induced to enter an overwintering condition by holding them through the summer and then subjecting them to a progressive reduction in temperature and photoperiod for 2 months. These frogs survived freezing for 48 hr at -3 degrees C. Their equilibrium ice content at this temperature was significantly lower (52.5%) than comparably treated summer animals. In the winter acclimatized group, frozen frogs had substantially higher blood glucose levels than unfrozen frogs (22.7 mumol/ml vs. 1.33 mumol/ml), but glycerol levels were not elevated after freezing. Freezing frogs conditioned for overwintering at -7 degrees C resulted in a higher equilibrium ice content (62.6%), but none survived. It is evident that in preparation for overwintering, frogs reduce the amount of ice formed at a given subzero temperature, but there is little indication of a substantial change in the total amount of ice tolerated.

Animals↗
PubMed1994

Characterization and subcellular distribution of G-proteins in highly purified skeletal muscle fractions from rabbit and frog.

The presence of G-proteins in highly purified fractions from frog and rabbit skeletal muscles was analyzed by Bordetella pertussis toxin-catalyzed ADP-ribosylation and by immunoblots. Two B. pertussis toxin substrates were present in transverse tubules and sarcoplasmic reticulum from frog and rabbit skeletal muscle. Immunoblot analysis suggested that the two B. pertussis toxin substrates present in rabbit sarcoplasmic reticulum are possibly alpha i2 and alpha i3, but the corresponding substrates in sarcoplasmic reticulum from frog are still unidentified. Transverse tubules isolated from both rabbit and frog also contained alpha i2 and alpha i3; additionally, beta 35, beta 36, alpha o (weak immunoreactivity), alpha i1 (and/or alpha i3 in frog), alpha s (short form only in frog), and alpha q were found. Sarcoplasmic reticulum from rabbit also contained alpha s (predominantly alpha s short), beta 36, and alpha q. The presence of alpha q in sarcoplasmic reticulum, in addition to transverse tubules, is potentially a very important finding since this G-protein has been described only in plasma membranes so far. Also, this study describes the candidate G-proteins for the control of excitation-contraction coupling in skeletal muscle.

Adenosine Diphosphate Ribose↗
PubMed1994

The pattern of catecholamine response to burst activity in leopard frogs, Rana pipiens.

It is well known that burst activity causes a rapid breakdown of muscle glycogen and extensive accumulation of lactate in frogs. During recovery, it has been shown that lactate is nearly totally recycled into muscle glycogen. Since catecholamines are likely to play some role in the regulation of postexercise repletion of muscle glycogen, the pattern of catecholamine response was assessed in frogs during intense physical activity and the ensuing recovery period. Chronically cannulated frogs were forced to swim until exhaustion, and serial blood samples were taken at regular time intervals for the measurements of catecholamines. The pattern of changes in plasma and muscle lactate and glucose and muscle glycogen during and after burst activity is similar to that reported in previous studies using noncannulated frogs, a result which indicates that the animals recover well from the surgical trauma associated with cannulation. The concentrations of plasma catecholamines in frogs at rest are comparable to those measured in other amphibians, and the levels of plasma epinephrine in resting frogs are much higher than those of norepinephrine. Burst activity causes a marked increase in plasma catecholamines, with higher levels reached by epinephrine. During recovery, the concentration of plasma catecholamines returns to normal within 30 min. Although this pattern of catecholamine response to intense physical activity may be favorable to the repletion of muscle glycogen postexercise, it remains to be clarified how critical the low levels and fast reduction in plasma catecholamines are for optimum glycogen resynthesis.

Animals↗
PubMed1985

Neuropeptide Y (NPY)-like immunoreactive amacrine cells in retinas of frog and goldfish.

The distribution of neuropeptide Y (NPY)-like immunoreactivity in rat, rabbit, chick, frog and goldfish retinas was investigated by immunohistochemistry. Positive results were observed only in the frog and goldfish retinas. NPY immunoreactivity was associated with a small population of amacrine cell bodies in the inner nuclear layer and cell processes in the inner plexiform layer of both retinas. In the frog retina, three distinct layers containing immunoreactivity were observed in the inner plexiform layer. In contrast, the immunoreactivity in the same area of the goldfish retina was more or less separated into two layers. Convincing evidence could not be found for the co-existence of NPY-like material with other putative transmitter-like substances in the two retinas. Radioimmunoassay revealed the presence of small amounts of NPY-like immunoreactivity in the rabbit retina; the goldfish and frog retinas contained significantly more immunoreactive material. High performance liquid chromatography of the immunoreactive material in frog and goldfish retinas showed each retina containing different molecular forms of NPY-like proteins, neither of which resembled porcine NPY or PYY. The endogenous NPY-like material of the frog retina can be released by potassium depolarisation in a calcium-dependent way. In view of all these data an NPY-like protein must now be considered a potential retinal transmitter.

Animals↗
PubMed1988

Lesion-induced vestibular plasticity in the frog: are N-methyl-D-aspartate receptors involved?

The synaptic excitation of central vestibular neurons in the isolated superfused brainstem of chronic hemilabyrinthectomized (HL) frogs and of controls was studied electrophysiologically and pharmacologically. Central vestibular neurons were excited either through vestibular afferent fibers or through the vestibular commissural pathway by means of electrical stimulation of the ipsilateral or the contralateral VIIIth nerve. In chronic HL frogs, commissural field potential amplitudes were on the average larger than those of intact frogs and the shape parameters of intracellularly recorded commissural EPSPs of chronic animals were on the average shifted towards those of vestibular afferent EPSPs. In control frogs, vestibular afferent EPSPs were generated independently from N-methyl-D-aspartate (NMDA) receptors, whereas commissural EPSPs exhibited a delayed NMDA receptor mediated component. Commissural EPSPs of HL frogs exhibited a NMDA receptor mediated component as well. The size of this EPSP component was larger when the time to peak of the EPSP was longer. EPSPs with similar rise times exhibited NMDA mediated components of similar size, irrespective of whether they originated from chronic animals or controls. The tendency of these EPSPs towards shorter rise times in chronic animals was paralleled by a similar decrease of the relative size of their NMDA receptor mediated component. It is concluded that the increased synaptic efficacy of commissural fibers observed in chronic HL frogs does not result from an increased NMDA receptor component.

2-Amino-5-phosphonovalerate↗
PubMed1993

The common frog (Rana temporaria) as a potential paratenic and intermediate host for Angiostrongylus vasorum.

Common frogs (Rana temporaria) were exposed either to third-stage larvae (L3) or to first-stage larvae (L1) of Angiostrongylus vasorum. Following exposure to L3, viable larvae could be detected in the frogs for at least 2 weeks. Following exposure to L1, the frogs developed viable L3 in their tissues within 30 days. In a test of the infectivity of these larvae, one fox was fed frogs previously infected with L3 and another fox was fed frogs previously infected with L1. On autopsy it was found that adult A. vasorum populations had been established in both foxes. Thus, it could be concluded that frogs can act not only as paratenic hosts but also as intermediate hosts for A. vasorum.

Angiostrongylus↗
PubMed1990

Characterization of kappa 1 and kappa 2 opioid binding sites in frog (Rana esculenta) brain membrane preparation.

The distribution and properties of frog brain kappa-opioid receptor subtypes differ not only from those of the guinea pig brain, but also from that of the rat brain. In guinea pig cerebellum the kappa 1 is the dominant receptor subtype, frog brain contains mainly the kappa 2 subtype, and the distribution of the rat brain subtypes is intermediate between the two others. In competition experiments it has been established that ethylketocyclazocine and N-cyclopropylmethyl-norazidomorphine, which are nonselective kappa-ligands, have relatively high affinities to frog brain membranes. The kappa 2 ligands (Met5)enkephalin-Arg6-Phe7 and etorphine also show high affinities to the frog brain. Kappa 1 binding sites measured in the presence of 5 microM/D-Ala2-Leu5/enkephalin represent 25-30% of [3H]ethylketocyclazocine binding in frog brain membranes. The kappa 2 subtype in frog brain resembles more to the mu subtype than the delta subtype of opioid receptors, but it differs from the mu subtype in displaying low affinity toward beta-endorphin and /D-Ala2-(Me)Phe4-Gly5-ol/enkephalin (DAGO). From our data it is evident that the opioid receptor subtypes are already present in the amphibian brain but the differences among them are less pronounced than in mammalian brain.

Amino Acid Sequence↗
PubMed2002

Isoforms of soluble alpha-tubulin in oocytes and brain of the frog (genus Rana): changes during oocyte maturation.

Rana oocytes have previously been shown to contain much more soluble tubulin than does the brain, suggesting different assembly and disassembly dynamics of frog oocyte tubulin compared to that in brain. By using centrifugation, SDS-PAGE, two-dimensional gel electrophoresis and Western blots, probed with anti-alpha-tubulin monoclonal antibodies, polymorphic alpha-tubulins (isoforms) were compared in brains and follicle-enclosed oocytes of northern (Rana pipiens) and southern (R. berlandieri) frogs. Oocyte tubulin in both species had isoforms with greater ranges of isoelectric point (pI) than those of brain tubulins; in particular, the oocyte tubulin pIs ranged further into the acidic region of the isoelectric-focusing gels than corresponding brain tubulin. This difference may, in part, be responsible for the previously reported assembly differences between oocyte tubulin (undetectable assembly) and brain tubulin (high assembly). Isoforms of alpha-tubulin with relatively acidic pI were more abundant in northern frog brain and oocyte soluble extracts than in analogous extracts from southern frogs. Furthermore, additional acidic alpha-tubulin isoforms were found in progesterone-treated oocytes (i.e., eggs), indicating increased heterogeneity of acidic alpha-tubulin isoforms during oocyte meiotic maturation. Among northern frog oocyte soluble components fractionated on Superose-6b columns, tubulin complexes with apparent molecular mass of about 1800 kDa were found to contain acidic alpha-tubulin isoforms while the putative oligomeric tubulins with an apparent molecular mass of about 250 kDa contained an additional relatively basic alpha-tubulin isoform. The acidic alpha-tubulin isoforms, therefore, are proposed to be associated with cold-adaptable cells of brain and oocytes, and may also be involved in stabilization of large soluble tubulin complexes in oocytes of the northern frog.

Animals↗
PubMed2005

Water relations of the burrowing sandhill frog, Arenophryne rotunda (Myobatrachidae).

Arenophryne rotunda is a small (2-8 g) terrestrial frog that inhabits the coastal sand dunes of central Western Australia. While sand burrowing is a strategy employed by many frog species inhabiting Australia's semi-arid and arid zones, A. rotunda is unique among burrowing species because it lives independently of free water and can be found nocturnally active on the dune surface for relatively extended periods. Consequently, we examined the physiological factors that enable this unique frog to maintain water balance. A. rotunda was not found to have any special adaptation to reduce EWL (being equivalent to a free water surface) or rehydrate from water (having the lowest rehydration rate measured for 15 Western Australian frog species), but it was able to maintain water balance in sand of very low moisture (1-2%). Frogs excavated in the field were in dune sand of 4.4% moisture content, as a consequence of recent rain, which was more than adequate for these frogs to maintain water balance as reflected by their low plasma and urine osmotic concentrations. We suggest that in dry periods of the year, A. rotunda can achieve positive water balance by cutaneous water uptake by burrowing deeper into the substrate to where the percent water content is greater than 1.5%.

Animals↗
PubMed1997

Changes in selected aspects of immune function in the leopard frog, Rana pipiens, associated with exposure to cold.

The effect of exposure to low temperatures (5 degrees C) on lymphocyte proliferation, leukocyte populations, and serum complement levels was examined in the northern leopard frog, Rana pipiens. Proliferation of T lymphocytes in response to phytohemagglutinin stimulation was significantly decreased in frogs kept for 2, 3, and 5 months at 5 degrees C compared to that of animals kept at 22 degrees C. A significant increase in the average percentage of neutrophils and a decrease in the mean percentage of eosinophils was observed in the blood of frogs held for 5 months in the cold compared to animals held at 22 degrees C for the same length of time. Mean serum complement activity after 1 month at 5 degrees C was significantly reduced in comparison to animals held at 22 degrees C and was not detectable after 5 months in the cold. Recovery of complement levels at room temperature (22 degrees C) was also examined after cold exposure. Complement levels were significantly higher than controls (at 22 degrees C) in frogs returned to 22 degrees C for 7 and 14 days after 5 months in the cold. After frogs were held at 5 degrees C for 1 month, serum complement levels increased significantly within 2 days after returning to 22 degrees C and continued to rise 5 and 9 days after warming. Injections with Aeromonas hydrophila following a 5-week exposure to 5 degrees C failed to cause death or observable symptoms of disease in frogs that were returned to 22 degrees C.

Adaptation, Physiological↗
PubMed1997

Differential effects of glycolytic and oxidative metabolism blockers on the Na-K pump in erythrocytes of the frog, Rana temporaria.

This study was undertaken to evaluate the effects of various metabolic blockers on the Na-K-pump activity and ATP content of frog erythrocytes. To eliminate K-Cl cotransport, the frog erythrocytes were incubated in nitrate media at 20 degrees C. Incubation of the red cells in a glucose-free medium for 2 h had no effect on cell ATP content and K+ influx measured as 86Rb uptake for 60 min. The Na(+)-K(+)-pump activity was also unchanged in the frog erythrocytes incubated in a glucose-free medium containing 10 mM 2-deoxy-D-glucose or adenosine. Unexpectedly, the treatment of red cells with 1-2 mM glycolytic blocker iodoacetate produced a 2-fold increase in the ouabain-sensitive K+ influx. The cell ATP content declined by 9.4% after 2 h of cell incubation with iodoacetate. Incubation of the red cells for 90 min in the presence of 2 mM cyanide, 0.01 mM antimycin A or 5 mM azide resulted in a significant reduction in K+ influx by about 50%, 45% and 32%, respectively. The cell ATP content diminished over 60 min and 120 min of cell incubation with 2 mM cyanide by 15.6% and 31.7% of control levels, respectively. In time-course experiments, a 50% reduction in the K+ influx was observed when the frog erythrocytes were incubated for only 30 min in the presence of 2 mM cyanide. In contrast, 0.01-0.10 mM rotenone, a site I inhibitor, and 0.01 mM carbonyl cyanide m-chlorophenylhydrazone, an uncoupler of oxidative phosphorylation were without effect on K+ influx into frog erythrocytes. These results indicate that about one-half of the Na(+)-K(+)-pump activity in frog erythrocytes is tightly functionally coupled to cytochromes via a separate "membrane-associated" ATP pool.

Adenosine↗
PubMed1998

Opposite effects of cooling on twitch contractions of skeletal muscle isolated from tropical toads (Leptodactylidae) and northern frogs (Ranidae).

Cooling increases the twitch force of frog skeletal muscle (Rana temporaria; Rana pipiens), but decreases the twitch force of tropical toad muscle (Leptodactylus insularis). Action potentials and intramembranous charge movement in frog and toad fibers were slowed identically by cooling. Cooling increased the integral of twitch Ca2+ detected by aequorin in frog fibers (1.4-fold), while also decreasing the peak and slowing the rate of decay. Conversely, cooling decreased the integral (0.6-fold) and the peak of twitch Ca2+ in toad fibers, without affecting the rate of decay. The difference in entire Ca2+ transients may account for cold-induced twitch potentiation in frogs and twitch paralysis in toads. In sustained contractions of toad fibers, cooling markedly decreased maximum force caused by: (i) tetanic stimulation, (ii) two-microelectrode voltage clamp steps, (iii) high [K+], or (iv) caffeine. Maximum force in sustained contractions was decreased moderately by cooling frog fibers. Rapid rewarming and simultaneous removal of high [K+] or caffeine during a sustained contraction, caused toad muscle force to rise towards the value corresponding to the warm temperature. This did not occur after removing high [K+] or caffeine from toad fibers kept in the cold. Transmission electron micrographs showed no relevant structural differences. Parvalbumins are thought to promote relaxation of frog muscle in the cold. The unique parvalbumin isoforms in toad muscle apparently lack this property.

Animals↗
PubMed2003

Exposure of leopard frogs to a pesticide mixture affects life history characteristics of the lungworm Rhabdias ranae.

We tested the hypothesis that exposure of leopard frogs ( Rana pipiens) to agricultural pesticides can affect the infection dynamics of a common parasite of ranid frogs, the lungworm Rhabdias ranae. After a 21-day exposure to sublethal concentrations of a pesticide mixture composed of atrazine, metribuzin, aldicarb, endosulfan, lindane and dieldrin, or to control solutions (water, dimethyl sulfoxide), parasite-free juvenile frogs were challenged with 30 infective larvae of R. ranae. Approximately 75% of the larvae penetrated the skin and survived in both exposed and control animals, suggesting that pesticides did not influence host recognition or penetration components of the transmission process. Rather, we found that the migration of R. ranae was significantly accelerated in hosts exposed to the highest concentrations of pesticides, leading to the establishment of twice as many adult worms in the lungs of frogs 21 days post-infection. Pesticide treatment did not influence the growth of lungworms but our results indicate that they matured and reproduced earlier in pesticide-exposed frogs compared to control animals. Such alterations in life history characteristics that enhance parasite transmission may lead to an increase in virulence. Supporting evidence shows that certain components of the frog immune response were significantly suppressed after exposure to the pesticide mixture. This suggests that the immune system of anurans exerts a control over lungworm migration and maturation and that agricultural contaminants can interfere with these control mechanisms. Our results also contribute to the ongoing debate regarding the role that anthropogenic factors could play in the perplexing disease-related die-offs of amphibians observed in several parts of the world.

Animals↗
PubMed1986

Phorbol diester treatment promotes enhanced adenylate cyclase activity in frog erythrocytes.

Incubation of intact frog erythrocytes with 12-O-tetradecanoyl phorbol-13-acetate (TPA), a tumor-promoting phorbol diester which activates protein kinase C, results in an approximate two- to threefold increase in subsequently tested beta-adrenergic agonist-stimulated adenylate cyclase activity. This increase is due to an elevation in the Vmax of the enzyme rather than to a change in affinity for the agonist. TPA treatment of frog erythrocytes does not alter the affinity (KD) or the binding capacity (Bmax) for the beta-adrenergic antagonist [125I]cyanopindolol. In addition, agonist/[125I]cyanopindolol competition curves are not affected by TPA pretreatment nor is their sensitivity to guanine nucleotides. Incubation of frog erythrocyte membranes alone with TPA does not promote sensitization or activation of adenylate cyclase activity. Pretreatment of intact frog erythrocytes with TPA also produces approximately two- to threefold increases in basal, guanine nucleotide-, prostaglandin E1-, forskolin-, NaF-, and MnCl2-stimulated adenylate cyclase activities in frog erythrocyte membranes. This enhancement of adenylate cyclase activity by TPA is induced rapidly (t1/2 approximately equal to 5 min) and with an EC50 of about 10(-7) to 10(-6) M. Other tumor-promoting phorbol diesters or phorbol diester-like compounds including 4 beta-phorbol 12,13-dibutyrate, 4 beta-phorbol 12,13-didecanoate, and mezerein are effective in promoting enhanced adenylate cyclase activity. In contrast, phorbols such as 4 beta-phorbol, 4 alpha-phorbol 12,13-didecanoate, and 4-O-methylphorbol 12-myristate 13-acetate, which are inactive in tumor promotion and which do not activate protein kinase C, do not affect frog erythrocyte adenylate cyclase activity. These data are suggestive of a protein kinase C-mediated phosphorylation of one of the adenylate cyclase components that is distal to the receptor, i.e., the nucleotide regulatory and/or catalytic components.

Adenylyl Cyclases↗
PubMed1980

Characterization of gastric mucosal membranes. II. Lipid compositions of purified gastric mitochondria from pig, rabbit and frog.

1. The lipid composition of purified mitochondrial fractions from the fundic mucosa of pig, rabbit and frog were determined. 2. The total lipids expressed as mg lipid per 100 mg mitochondrial protein were approx. the same in pig and rabbit (13.4 and 15.5, respectively) and much higher than in frog (8.5). 3. The levels of phospholipids were about the same in pig and frog (approx. 61% of the total lipid) and lower than rabbit (78%). However, the levels of cholesterol were significantly different in the three species and constituted 22, 9 and 18.2% of the total lipids in pig, rabbit and frog mitochondria, respectively. 4. The glycolipid content in the mitochondrial lipids from pig, rabbit and frog were 7, 5.6 and 10.5%, respectively. 5. Cardiolipin contributed from 5.6 to 7.5% of the total phospholipids in the various species. Phosphatidylethanolamine and phosphatidylcholine together accounted for 80 90% of the total phospholipids in the various species; the contribution of phosphatidylcholine being always higher than that of phosphatidylethanolamine. Small but significant amounts of phosphatidylinositol were present in all species. 6. Generally, the predominant saturated fatty acid in the phospholipids was 16:0 from all species (except in phosphatidylethanolamine from pig and frog), and 18:1 and 18:2 were the predominant unsaturated fatty acids from all species. Sphingomyelin contained the highest amount of saturated fatty acids (over 80%) in both the species (pig and rabbit) studied.

Animals↗
PubMed1983

Neutral lipids of frog and rat rod outer segments.

Neutral lipids of rod outer segments (ROS) from frog and rat comprise roughly 10 mol% of the total lipids and consist of free sterol, free fatty acids, and 1,2-diglycerides, but contain no detectable sterol esters or triglycerides. Expressed as nmol per mg ROS protein, the levels of both free fatty acids and free sterol are higher in the rat than in the frog, whereas the diglycerides in frogs are about four times higher than in rats. The level of 22:6 omega 3 in the free fatty acids fraction of the frog is twice that of the rat, although the level of 22:6 omega 3 in both the frog and rat free fatty acids is lower than in any of the glycerolipids. The diglyceride fraction from both animals consists almost entirely of two molecular species: in the frog, the C-38 and C-40 type predominate in a molar distribution of 52 and 42% respectively, whereas in the rat, the C-36 and C-38 types are most abundant in a molar distribution of 28 and 60%, respectively. Comparison of the diglyceride fatty acid and molecular species compositions with those of phosphatidylinositol and phosphatidic acid led to the suggestion that ROS diglycerides are derived from phosphatidylinositol.

Animals↗
PubMed1983

Effect of Tyr-Pro-Leu-Gly-NH2 on melanotropin-stimulating hormone release in the frog and rat.

The tetrapeptide Tyr-Pro-Leu-Gly-NH2 (Tyr-MIFI) has been recently characterized in the hypothalamus and pineal of the rat. Since the concentration of Tyr-MIFI in the brain is increased by pinealectomy and is higher when the animals are in the dark, the possibility that Tyr-MIFI could be a physiological regulator of melanotropin secretion has been investigated. For this study a well-defined perifusion model has been applied, using whole neurointermediate lobes from male frogs (Rana ridibunda Pallas) or male Wistar rats. The amount of alpha-MSH released in the effluent perifusate was measured by means of a sensitive and specific radioimmunoassay method. For concentrations ranging from 10(-10) to 10(-6) M, Tyr-MIFI did not significantly alter the spontaneous release of alpha-MSH in the frog nor did it alter the release of alpha-MSH in the rat. Since it has been recently demonstrated that the tripeptide pGlu-His-Pro-NH2 (mammalian TRH) is a specific MSH-releasing factor in the frog, the possibility that Tyr-MIFI could modulate the response of the intermediate lobe of the frog to TRH has also been investigated. No alteration of TRH-induced alpha-MSH release was observed in the presence of a 100-fold excess of Tyr-MIFI. In addition, Tyr-MIFI was found to be unable to lighten the skin of the frog (Rana pipiens) when applied directly to the pituitary of the darkened animals. Thus these results definitively rule out the possibility that Tyr-MIFI is the melanotropin-release inhibiting factor in the frog or rat.

Animals↗