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At least 19 recordsLinked to original sources
PubMed1988

Reversible effect of depolarization by K-propionate on sub-miniature endplate potential to bell-miniature endplate potential ratios, on miniature endplate potential frequencies and amplitudes, and on synaptic vesicle diameters and densities in frog neuromuscular junctions.

Miniature endplate potentials were recorded from edge muscle fibers of frog sartorius muscles during high frequencies induced with K-propionate and during recovery. The identified neuromuscular junctions were studied with the electron microscope and their ultrastructure was correlated with amplitude and numbers of miniature endplate potentials generated. Miniature endplate potential amplitudes were maintained during the first 10 min of depolarization. They then decreased during the next 2-3 h until the mode was lost to the noise. Miniature endplate potential frequency was greatly increased during the first hour and there was initial depletion of vesicles. Miniature endplate potential frequencies remained high (5 x 10(5)/h) for 3 h but vesicle densities returned to nearly normal values during the second to third hour of treatment. The conspicuous infolding of the presynaptic membrane noted during the first hour of treatment suggests that recycling of vesicles is initially slower than fusion. Calculated recycling time is shorter than 25 min. During recovery after prolonged K-propionate treatment, the sub-miniature endplate potential class reappeared within minutes but about 20 min were required before it returned to control size. Subsequently, the bell-miniature endplate potentials reappeared and slowly increased in amplitude. The ultrastructure returned to a normal state. There was no change in vesicle diameters. No significant difference was found between the diameters of "touching vesicles" (vesicles touching the presynaptic membrane) and the non-touching vesicles. By comparison, lanthanum ions (1 mM) released a smaller number of quanta which did not exceed the number of vesicles present at the start of the experiment. Variations of the subunit hypothesis of the quantum of transmitter release are discussed.

Action Potentials↗
PubMed1996

Hypertonic treatment reversibly increases the ratio of giant skew-miniature endplate potentials to bell-miniature endplate potentials.

Miniature endplate potentials were recorded from single frog muscle fibers before, during and after treatment with hypertonic saline (200-500 mM NaCl or Na gluconate added to frog saline). Miniature endplate potential amplitude distributions were plotted from small muscle fibers so that the modes and ratios of the skew-miniature endplate potential to bell-miniature endplate potential classes could be defined. Muscle fibers were voltage clamped with two electrodes to determine the input resistance before, during and after treatment. Input resistance increased from two to 100 times during treatment and rapidly fell towards control values (no more than 30% greater) when preparations were returned to normal frog saline. Short duration treatments with 200-300 mM hypertonic salines immediately increased frequencies (100-fold) of both skew-miniature endplate potential and bell-miniature endplate potential classes. Preparations when returned to normal frog saline after a few minutes of treatment showed control miniature endplate potential distributions within minutes. One to two hour treatments left only the skew-miniature endplate potential class and with hour-long recovery periods bell-miniature endplate potentials reappeared and ratios of skew-miniature endplate potential to bell-miniature endplate potential classes returned to control values. Treatment with 500 mM NaCl added to frog saline immediately increased the percentage of skew-miniature endplate potentials (from 2 to 50%) with little or no increase in overall miniature endplate potential frequencies. The mode of the skew-miniature endplate potential class was unchanged after hypertonic treatment, whereas that of the bell-miniature end plate potential class either remained about the same size or decreased depending on the duration of treatment. The number and percentage of giant-miniature endplate potentials belonging to the skew-miniature endplate potential class increased as a function of the duration of 200-300 mM hypertonic saline treatments. Most giant-miniature endplate potentials had a slow rising phase with a foot and/or breaks demonstrating a composite structure. Sequentially recorded giant-miniature endplate potentials had similar initial slopes indicating either repetitive releases from single sites or releases from cooperative sites. After hypertonic treatment the bell-miniature endplate potential size was never more than that expected with the increase (under 30%) in input resistance. The results presented here are completely different from those of Yu and Van der Kloot [(1991) J. Physiol. 433, 677-704] who reported that the bell-miniature endplate potential amplitude was increased two- to four-fold after hypertonic treatment. The wide range of results in the ratio of skew-miniature endplate potential to bell-miniature endplate potential classes is discussed in regards to the quantal hypothesis which is based on a single class of immutable amounts of transmitter; and, a hypothesis based on a dynamical process that meters transmitter in subunit amounts to control miniature endplate potential size and class during release.

Animals↗
PubMed1987

Description of the sub-miniature endplate potential distribution, determination of subunit size and number of subunits in the adult frog neuromuscular bell-miniature endplate potential.

Miniature endplate potentials were recorded from the isolated pectoralis cutaneous muscle of the frog during very stable recording conditions and low noise levels. Two to 5 x 10(3) miniature endplate potentials were filmed at eight unstressed junctions that met rigorous experimental criteria for analysis. Seven junctions generated enough sub-miniature endplate potentials (1-3%) to produce a bell-shaped amplitude distribution. The sub-miniature endplate potential means were usually 9-10 times smaller than the modal bell-miniature endplate potential values. The standard deviation of the sub-miniature endplate potential class was calculated by subtracting the noise and measurement error from the measured sub-miniature endplate potential distribution. The coefficients of variation of the sub-miniature endplate potential distribution were 9-16%. Half of the bell-miniature endplate potential amplitude distributions showed 4-6 integral peaks in the central part of the distributions and the positions of these peaks were maintained with increasing sample size. The remaining distributions were not smooth and suggested integral peaks. The intervals between the peaks were about the same size as the sub-miniature endplate potential mode. These data provide further evidence for the subunit hypothesis of the quantum of transmitter release and describe the amplitude distribution of the sub-miniature endplate potential class of the adult preparation.

Action Potentials↗
PubMed2001

[Analysis of genetic diversity of Bama miniature pigs and Guizhou miniature pigs by RAPD].

RAPD analysis was performed with 31 selected single primers to study genetic diversity of two strains of miniature pigs, The percentages of polymorphisic loic in or between two strains of miniature pigs were 30.9%, 29.2% and 25.7% respectively, and the average genetic distances in and between two strains of miniature pigs were 0.120, 0.072, and 0.067 respectively. These results suggested that genetic diversity and genetic variability were poorer in and between two strains of miniature pigs than ordinary breeds' pigs.

Animals↗
PubMed1990

Cardiac function and morphology of Hanford miniature swine and Yucatan miniature and micro swine.

The use of miniature swine in biomedical research is increasing; however, a comparison of cardiac function and morphology between strains has yet to be characterized. The purpose of this project was to examine comprehensive hemodynamics and cardiac morphology of three groups of ten normal, 4 months old, age-matched Yucatan miniature (MINI) pigs, Yucatan micropigs (MICRO) and Hanford (HAN) miniature pigs, 5 males and five females per group. Closed chest cardiac catheterization under equivalent conditions was performed followed by post mortem cardiac morphometry. Mean arterial pressure was significantly greater in the Hanford group when compared to both the minipig and micropig pigs (HAN: 89 +/- 4; MINI: 48 +/- 3; MICRO: 53 +/- 2 mmHg). Pulmonary vascular resistance was significantly different between the three groups (HAN: 9 +/- 1; MINI: 60 +/- 12; MICRO: 111 +/- 29 dyne x sec/cm x m2). The Hanford strain had a significantly smaller heart weight to body weight ratio than the other two groups (HAN: 4.6 +/- 1.0; MINI: 5.7 +/- 0.1; MICRO: 5.5 +/- 1.0). Variations in cardiovascular parameters occur among these strains and should be considered when constructing experimental designs.

Animals↗
PubMedDate not supplied

Hyperlipemia in 9 miniature horses and miniature donkeys.

The medical records from 9 consecutive miniature horses (n = 5) and miniature donkeys (n = 4) with hyperlipemia (serum triglyceride concentration > 500 mg/dL) were reviewed. In all cases, hyperlipemia was a secondary complication of a primary systemic disease including septicemia, colitis, parasitism, esophageal obstruction, gastric impaction and rupture, fecalith, and pituitary adenoma. Therapy consisted of specific treatment for the primary disease, supportive care, and nutritional support. The mean time for resolution of hyperlipemia in cases requiring nutritional support (n = 6) was 7 days, and the duration of nutritional support in surviving patients was 11.7 days. Seven of 9 patients survived. The primary disease resulted in death in 2 patients. Enteral feeding with commercially prepared low residue diets and treatment of the primary disease was successful in reversing hyperlipemia in 5 of 6 surviving patients that required nutritional support. Parenteral administration of a glucose-based (non-lipid) solution was successful in resolving hyperlipemia in 1 patient.

Animals↗
PubMed1993

[Initial characterization of a new miniature animal model in the rat: studies on anatomy, pituitary hormones and GH mRNA in miniature rat Ishikawa].

Miniature rat Ishikawa (MRI) is an experimental model for pituitary miniaturism with an autosomal recessive mode of inheritance. This paper reports the discovery and initial characterization of a new mutant rat. The mutation arose spontaneously in a breeding colony of Wistar rats at the Ishikawa Animal Laboratory (Saitama). Body growth in MRI was retarded in 56% and 71% of normal control rats for males and females, respectively. In immunohistochemical studies for anterior pituitary sections, GH secreting cells were reduced in the amounts and the intensity of stain in MRI compared with normal control rats. There was no detectable difference in the amounts or distribution of LH, FSH, PRL, TSH and ACTH between MRI and normal control rats. MRI showed a selective reduction in pituitary GH contents and in response to human GRH. Pituitary GH contents were approximately 31% of normal in males and 45% in females. Pituitary TSH contents and serum TSH levels were within the normal range in MRI. Total T3 and T4 levels were also within the normal range in MRI. Pituitary total mRNA extracts revealed that GH message in male MRI was reduced in 53% of normal control rats, and that fragment size of GH mRNA was within the normal range. The immunohistochemical findings, supported by a reduced GH content in pituitary extracts and low GH response to GRH, were compatible with a deficiency of GH caused by a reduced expression of pituitary GH mRNA. MRI, which showed a selective pituitary GH deficiency, may provide a useful new model for studying the endocrinological aspects of the growth.

Animals↗
PubMed1970

Miniature cell culture systems for use in field isolation of viruses: cell stability and sensitivity to selected laboratory-propagated viruses during storage in miniaturized environments.

Cell cultures were miniaturized in 1-dr vials or in capillary tubes (100 by 3 mm) and examined for their capacity to maintain normal gross morphology and sensitivity to infection by viruses during storage under a variety of conditions. The purpose of these studies was to determine the feasibility of using such cultures in the field during epidemiological investigations. From the results of this work it was concluded that such a feasibility exists.

Animals↗
PubMed1981

Transplantation in miniature swine. VIII. Recombination within the major histocompatibility complex of miniature swine.

Offspring of heterozygous parents derived from three herds of miniature swine, each of which is homozygous at the major histocompatibility complex (MHC), were screened for recombination within the MHC. The swine were typed serologically at weaning and later typed by mixed lymphocyte reaction (MLR). Two intra-MHC recombinants were discovered, both of which involved the exchange of D region specificities without apparent dissociation of ABC region specificities, confirming the localization of the SLA-D region outside of the SLA-ABC regions. The first recombinant was the offspring of an SLAc/d (cd) by dd mating and typed serologically as cd but typed by MLR as dd. The second recombinant was the offspring of a cd by cd mating. It typed serologically as cc but stimulated cc in one-way MLR and retained its reactivity to dd, thus suggesting a possible recombination within the D region. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of 3H-leucine-labeled lymphocyte surface antigens demonstrated that corresponding Ia antigens were also exchanged during these recombinant events supporting the hypothesis that genes coding for Ia antigens are identical or closely linked to D region genes encoding the MLR specificities.

Animals↗
PubMed1981

[Hematochemical characteristics of miniature pig Göttingen (miniature pig G) (author's transl)].

The biochemical components, enzymes, and other items from the sera and plasma of normal male and female Göttingen miniature pigs from 3 to 20 months of age were investigated. The data were compared with the normal biochemical values of rhesus monkeys, beagle dogs, and JCL: SD rats. The following characteristics were noted. 1. Activities of serum enzymes were higher and their normal ranges wider than in the other experimental animal sera. 2. Of lipid components measured, total cholesterol and phospholipid showed strikingly lower values than in the monkey and the dog. 3. The serum urea nitrogen levels were lower than in the other experimental animal sera. 4. Serum creatinine and potassium were present at relatively high levels, with wide normal ranges. 5. There was a tendency with advancing age toward lower alkaline phosphatase and higher total protein and creatinine. 6. Leucine aminopeptidase was higher while total cholesterol and phospholipid were lower, in the male than in the female. 7. The electrophoretic patterns of serum protein and lipoprotein differed markedly among the species.

Animals↗
PubMed1991

Characteristics of slow-miniature endplate currents show a subunit composition.

The normal neuromuscular junction shows two classes of spontaneous miniature endplate potentials. These classes are based on a discontinuity in the profile of miniature endplate potential amplitude distributions. The amplitude of one class of miniature endplate potentials from a bell-shaped amplitude distribution and the remaining miniature endplate potentials compose a population which forms a left-hand skew distribution with a mode 1/7 to 1/10 that of the bell-miniature endplate potentials [Kriebel M. E. and Gross C. E. (1974) J. gen. Physiol, 64, 85-103]. Some skew-miniature endplate potentials have a slow time-to-peak and show breaks on the rising phase. Most treatments that alter the miniature endplate potential frequency change the ratio of skew-miniature endplate potentials/bell-miniature endplate potentials [Kriebel M. E. et al. (1976) J. Physiol. 262, 553-581]. The time characteristics of miniature endplate currents were readily altered in the isolated frog and mouse neuromuscular junctions with several agents known to increase the percentage of slow-miniature endplate potentials (heat, botulinum toxin, 4-aminoquinoline and increases in bath osmolarity). The slow-miniature endplate potential amplitudes were a continuum of amplitudes from skew- to giant miniature endplate potentials. The rising phases of miniature endplate potentials were a continuum from smooth to many with breaks and offsets. In a series of sequentially recorded slow-miniature endplate currents, many had congruent rising phases of constant slope regardless of amplitude or of time-to-peak. The rising phases of congruent slow-miniature endplate currents which showed a change in slope deviated at similar amplitudes. The least value of the slope of a slow-miniature endplate current was that of the sub-miniature endplate current; and, miniature endplate currents with overall lower slope values showed a wave pattern and/or irregular breaks which suggests summation of sequentially delayed sub-miniature endplate currents. Plots of the amplitude vs time-to-peak of miniature endplate currents from identified junctions demonstrated that the normal percentage of slow-miniature endplate currents was greatly increased with the treatments used here and that the time-to-peak of giant miniature endplate currents usually was longer than that of normally occurring bell-miniature endplate currents. Giant miniature endplate currents with short time-to-peak values are probably from two miniature endplate currents occurring, by chance, almost simultaneously. During and/or after treatments, miniature endplate currents formed clusters of similar size miniature endplate currents, not randomly distributed in time, which graded from distinct miniature endplate currents to giant miniature endplate currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2004

Miniature intracardiac assist device provides more effective cardiac unloading and circulatory support during severe left heart failure than intraaortic balloon pumping.

BACKGROUND: Hemodynamic assistance with a miniature intracardiac pump may fill the treatment gap between use of an intraaortic balloon pump (IABP) and the current, more invasive ventricular assist devices. The objective of this study was to compare the hemodynamic efficacy of a miniature intracardiac pump device with that of IABP. METHODS AND RESULTS: Reversible acute mitral regurgitation (AMR) was induced in eight calves by stenting the mitral valve using a vena cava filter. Full and partial AMR assist were compared with maximum IABP support in each animal. In full-support mode, both assist systems increased cardiac output (miniature intracardiac pump, 13% [p < 0.05]; IABP, 3% [p < 0.05]), mean aortic pressure (miniature intracardiac pump, 13% [p < 0.05]; IABP, 8% [p < 0.05]), carotid artery flow (miniature intracardiac pump, 29% [p < 0.05]; IABP, 5% [difference not significant]), and coronary blood flow (miniature intracardiac pump, 25% [difference not significant]; IABP, 34% [p < 0.05]). Again in full-support mode, both systems reduced left atrial pressure (miniature intracardiac pump, 2.4 mm Hg [p < 0.05]; IABP, 0.7 mm Hg [p < 0.05]), peak left ventricular (LV) pressure (miniature intracardiac pump, 13% [p < 0.05]; IABP, 5% [p < 0.05]), and external LV work (miniature intracardiac pump, 29% [p < 0.05]; IABP, 3% [p < 0.05]). Only full miniature intracardiac pump support reduced both end-diastolic LV volume (7%; p < 0.05) and end-systolic LV volume (10%; p < 0.05). IABP mainly improved coronary perfusion, while the miniature intracardiac pump proved more capable of genuinely unloading the LV. CONCLUSIONS: We conclude that during severe acute LV failure, the miniature intracardiac pump is capable of more effective cardiac unloading and circulatory support than IABP.

Acute Disease↗
PubMed1985

Characterization of miniature inhibitory post-synaptic potentials in rat spinal motoneurones.

Intracellular recordings were made from motoneurones in the isolated spinal cord of neonatal rats. After action potentials had been abolished by tetrodotoxin (TTX, 10(-6) g/ml), small (approximately 0.4 mV) depolarizing potentials occurred spontaneously in motoneurones at low frequencies (approximately 1.5 Hz). These potentials were detectable only after the intracellular Cl- concentration of motoneurones was raised by using KCl electrodes and most of them were blocked by strychnine, suggesting that they are inhibitory post-synaptic potentials (i.p.s.p.s). These spontaneous i.p.s.p.s under TTX are designated as 'miniature i.p.s.p.s' in order to distinguish them from i.p.s.p.s arising from spontaneous impulse activities of interneurones or afferent fibres. The miniature i.p.s.p.s were still observed after Ca2+ in saline was substituted by Mg2+ or Mn2+. In low Ca2+ and high Mg2+ saline, the amplitude distribution of miniature i.p.s.p.s was essentially the same as in normal saline. The frequency of miniature i.p.s.p.s increased when external Ca2+ concentration was raised. The frequency decreased to about 60% of the control when external Ca2+ was substituted by Mg2+ (2-4 mM), whereas it increased to more than 20-fold when substituted by Mn2+ (3-5 mM). When the external K+ concentration was raised, the frequency of miniature i.p.s.p.s under TTX increased non-linearly with the K+ concentration. The maximum slope in the relation between the log frequency and log K+ concentration was about 3.6. When the osmotic pressure was increased by adding sucrose, miniature i.p.s.p.s increased in frequency. The effect of osmotic pressure was relatively mild compared with that reported for the miniature end-plate potentials (e.p.p.s) in the frog. When the temperature was raised, the frequency of miniature i.p.s.p.s increased. The relation between frequency and temperature fitted approximately to a straight line in Arrhenius plot with a Q10 of about 2.6. These characteristics of the miniature i.p.s.p.s closely resemble those of the miniature e.p.p.s. It is concluded that the miniature i.p.s.p.s recorded in motoneurones are equivalent in nature to the miniature e.p.p.s in neuromuscular junctions, thus reflecting the spontaneous release of quantal packages of the inhibitory transmitter.

Action Potentials↗
PubMed1990

The effects of L-vesamicol, an inhibitor of vesicular acetylcholine uptake, on two populations of miniature endplate currents at the snake neuromuscular junction.

The actions of the active L-isomer of vesamicol, an inhibitor of the vesicular storage of acetylcholine, has been studied on spontaneous and evoked acetylcholine release at the snake neuromuscular junction. Miniature endplate currents and endplate currents were recorded from cut muscle fibres of the garter snake, Thamnophis sirtalis. In controls, prolonged periods of high frequency nerve stimulation produced a bimodal distribution of miniature endplate current amplitudes. The stimulation induced "small-mode" miniature endplate currents had a mean amplitude of around 40-55% of the pre-stimulation miniature endplate current. Relative to the normal-sized post-stimulation miniature endplate current, the proportion and, to a lesser extent, amplitude of the small-mode miniature endplate currents was related to both the frequency and duration of nerve stimulation and to the extracellular calcium ion concentration. In unstimulated preparations, L-vesamicol (2-5 microM) did not affect either endplate current quantal content or miniature endplate current amplitude or frequency. However, at these doses, the mean amplitude of the stimulation-induced, small-mode miniature endplate current was reduced by L-vesamicol in a concentration-dependent manner such that they were not visible at the highest dose. L-Vesamicol had no affect on the mean or coefficient of variance of amplitude of the larger, normal-sized miniature endplate current. Additionally, the stimulation-induced increase in overall miniature endplate current frequency seen in controls was abolished by 5 microM L-vesamicol. After prolonged 10 Hz nerve stimulation endplate current amplitude was markedly reduced in both controls (by 94%) and in the presence of 5 microM L-vesamicol (by 98%). Analysis of endplate current amplitude variance showed that in control the decrease was due to reductions in both quantal content and quantal size while in L-vesamicol the decrease was due entirely to a change in quantal content with no change in quantal size. Thus, we have observed that L-vesamicol selectively reduces the amplitude of a population of stimulation-induced small-mode quanta both as miniature endplate currents and as constituents of endplate currents. We suggest that these quanta are derived from a highly active, readily releasable pool. An action of L-vesamicol on this labile pool is consistent with previous observations on its ability to inhibit the vesicular storage of acetylcholine.

Acetylcholine↗
PubMed1991

Evaluation of urine and serum metabolites in miniature schnauzers with calcium oxalate urolithiasis.

To evaluate underlying causes of calcium oxalate urolithiasis, 24-hour excretion of urine metabolites was measured in 6 Miniature Schnauzers that formed calcium oxalate (CaOx) uroliths during periods when they were fed a standard diet and during periods when food was withheld. Serum concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D also were evaluated. Serum calcium concentrations were normal in all 6 affected Miniature Schnauzers; however, during diet consumption, mean 24-hour urinary excretion of calcium was significantly (P = 0.025) higher than calcium excretion when food was withheld. In 1 dog, urinary calcium excretion was lower during the period of food consumption, compared with the period when food was withheld. Compared with clinically normal Beagles, Miniature Schnauzers that formed CaOx uroliths excreted significantly greater quantities of calcium when food was consumed (P = 0.0004) and when food was withheld (P = 0.001). Miniature Schnauzers that formed CaOx uroliths excreted significantly less oxalate than clinically normal Beagles during fed (P = 0.028) and nonfed (P = 0.004) conditions. Affected Miniature Schnauzers also excreted abnormally high quantities of uric acid. Excretion of citrate was not different between Miniature Schnauzers with CaOx urolithiasis and clinically normal Beagles. In 5 of 6 Miniature Schnauzers with CaOx urolithiasis, concentrations of serum parathyroid hormone were similar to values from age- and gender-matched Miniature Schnauzers without uroliths. The concentration of serum parathyroid hormone in 1 dog was greater than 4 times the mean concentration of clinically normal Miniature Schnauzers. Mean serum concentrations of 1,25-dihydroxyvitamin D in Miniature Schnauzers with calcium oxalate urolithiasis were similar to concentrations of clinically normal Miniature Schnauzers.

Animals↗
PubMed1989

Reappearance of miniature endplate potentials in frog neuromuscular junctions "silenced" by lanthanum ions.

Miniature endplate potentials and currents were recorded from frog sartorius muscle fibres. As expected from previous work, La3+ caused a very large increase in miniature endplate potential frequency, followed by a progressive decrease, ending in the virtually complete disappearance of miniature endplate potentials. Soon after its application, La3+ caused an increase in the amplitude of miniature endplate potentials due to a lengthening of the underlying miniature endplate currents. Analysis of membrane current fluctuations produced by acetylcholine showed that La3+ caused an increase in the lifetime of the channels opened by acetylcholine. After miniature endplate potentials had vanished following La3+ treatment, the muscles were placed in organ culture conditions to see if miniature endplate potentials would reappear. After several hours miniature endplate potential activity was resumed in about 25% of the endplates, and disappeared again a few hours later, presumably because of accelerated nerve terminal degeneration. Preliminary electron microscopic observations suggest that the recovery of miniature endplate potential activity was accompanied by re-formation of synaptic vesicles in the motor endings.

Animals↗
PubMed1991

Endocrine characteristics of a miniature condition in Brahman cattle: circulating concentrations of some growth-related hormones.

Four miniature Brahman calves born in 1988 and 1989, along with four contemporary sex-matched Brahman control calves, were used in experiments to determine circulating concentrations of insulin-like growth factor I (IGF-I), growth hormone (GH), insulin, triiodothyronine, and thyroxine, and plasma glucose response to insulin challenge. The effect of plane of nutrition on plasma concentrations of IGF-I and insulin was also determined and a clinical screen of blood chemistries was conducted to determine effects of calf type. Plasma IGF-I was six times higher in control calves compared with miniature calves (209.0 vs 35.0 ng/ml; P = 0.001). However, miniature calves had mean plasma GH about six times higher (37.8 vs 6.2 ng/ml; P = 0.004) and had twice as many secretory episodes (9 vs 4.5; P = 0.005) over an 8-hr sampling period. Plasma concentrations of triiodothyronine (2.54 vs 1.80 ng/ml) and thyroxine (88.8 vs 56.2 ng/ml) were higher in control compared with miniature calves (P = 0.001), but concentrations of triiodothyronine and thyroxine in both calf types were within normal ranges. Although miniature calves displayed similar plasma glucose concentrations to controls, hypoglycemic response to insulin challenge tended to be greater in miniature calves. Nutritional regulation of circulating IGF-I appeared to be intact in miniature as well as control calves, as evidenced by a reduction in plasma IGF-I concentration following a decrease in plane of nutrition, and a subsequent increase in plasma IGF-I concentration following realimentation. Serum urea nitrogen was lower (P = 0.02) in control compared with miniature calves. These data describe a miniature condition in Brahman cattle that is manifested by apparently normal proportioned growth but small stature, and that is associated most notably with abnormally low circulating concentrations of IGF-I in the presence of paradoxically high circulating concentrations of GH. This condition appears to be similar to Laron dwarfism in humans, in which the low IGF-I is caused by an abnormality in the GH receptor.

Animals↗