Intact Pigs Research Articles

PAF and the role of the vagus nerve in the breathing pattern of the pig

In 14 anesthetized, spontaneously breathing pigs we examined the changes in breathing pattern, in respiratory mechanics and in systemic and pulmonary vascular parameters after i.v. PAF administration. In another 3 pigs, the effects of PAF were also examined after bilateral vagotomy. In intact pigs, PAF induces apnea, bronchoconstriction, pulmonary hypertension and systemic hypotension. Our results also show that administration of PAF alters the phasic vagal activity, modifying the slope of V T vs T I and T E vs T I relationships and the T I † T I ratio. These effects and apnea are vagus-dependent. The central excitatory timing effect of PAF on inspiratory duration (T I †) was correlated with a decrease in passive compliance but not with active compliance. We postulate that the activation by vagal input strengthens the mechanisms that counteract the bronchoconstrictor effect of PAF.

The use of the mobile bag technique in swine. Determination of the apparent crude protein digestibility and amino acid absorption of feed and rations

The mobile bag technique (MBT) was used in two ileorectostomized and two intact pigs with duodenal cannulae, in order to estimate the precaecal and total crude protein digestibility and amino acid (lysine, methionine, cystine, threonine, tryptophan) absorption of ten single feedstuffs (field bean, lupin, rapeseed meal, fish meal, barley, wheat) and three diets. For each feed 36 bags were applied per animal. After a peptic predigestion in vitro, application of the bags through the duodenal cannula into the intestine and their passage through the gut, the residues remaining in the bags were pooled to collective samples and just as the original feed material analysed on dry matter, nitrogen and amino acids. The directly determined MBT-digestibilities (BV) and the values obtained by regressive calculations (BVb) have been compared with apparent digestibilities (sV) conducted from conventional digestion experiments. 74 per cent of all BV data was higher than the corresponding sV values. Similarities of BV with sV showed in 58 per cent, those of BVb with sV only in 17 per cent. In all cases differences of > +/- 4 digestibility units showed. Checking additivity of diet-BV by means of calculations from the BV of their single ingredients did not generally lead to the same results as the directly estimated diet-BV; in some cases the results were contrary. Therefore the use of MBT for mixed feed diets has to be further investigated. For single feedstuffs the MBT can be used successfully as a rapid and simple technique when regressive calculations are employed.

Estrogen receptor-immunoreactive glia, endothelia, and ependyma in guinea pig preoptic area and median eminence: electron microscopy.

The presence of estrogen receptors (ERs) in nonneural cells in brain, including glia, ependyma, and endothelia, has not previously been documented with electron microscopy. This study employed immunocytochemistry to investigate whether ER immunoreactivity (ER-ir) is present in glial, ependymal, or endothelial cells in the medial preoptic area (POA) and median eminence (ME) in the brain of gonadally intact female guinea pigs. Tissue sections through these regions were immunostained with monoclonal antibody H222 for ER localization using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogen. ER-ir cells were identified ultrastructurally by the presence of distinct spicule-like TMB crystals in nuclei. While neurons constituted the clear majority of ER-immunopositive cells, labeled astrocytes, ependyma, and endothelia were also present. Distinct intranuclear TMB crystals were present in astrocytes at the anterior pole of the POA within the preventricular periventricular nucleus, anterior compact subnucleus of the medial preoptic nucleus (MPNa), and organum vasculosum of the lamina terminalis, indicating ER-ir. In the MPNa, cell counts performed at the ultrastructural level revealed that 9.6% (15 of 156) of the astrocytes were ER-ir. To further explore the relationship of ERs with astrocytes, ER/glial fibrillary acidic protein (GFAP) double labeling experiments were performed using TMB and diaminobenzidine tetrahydrochloride for ER and GFAP localization, respectively. These studies verified the presence of ERs in astrocytes at the anterior pole of the POA and demonstrated the presence of ERs in GFAP-ir cells in the ME. Cell counts at the ME showed that 23 of 50 (46%) GFAP-ir cells were ER-ir. ER-ir was also present in scattered ependymal cells lining the third ventricle at the POA and overlying the ME. Typically, approximately four to eight ER-ir ependymal cells were present around the perimeter of the third ventricle, although occasionally small aggregations of greater numbers of labeled cells were observed. Both common ependyma and cells morphologically identified as tanycytes were ER-ir. Some endothelial cells and vascular smooth muscle cells also contained ERs. While approximately 11% of the vessels were lined by ER-ir cells in sections through the MPNa and preventricular periventricular nucleus, approximately 15% of the vessels were labeled in the organum vasculosum of the lamina terminalis. In the ME a greater percentage (59%) of the vessels contained ER-ir endothelial cells. Collectively, these results indicate that in addition to regulating the activity of neurons, estrogen may affect brain function through effects exerted on astrocytes, ependymal cells, and endothelial cells.

Studies of the digestibility of pigs fed dietary sucrose, fructose or glucose.

Digestion of sucrose, fructose and glucose was studied in pigs with reentrant cannulas in the distal ileum or intact pigs fed diets formulated with sucrose, fructose and glucose as the major energy source and torula yeast. Sucrose and glucose were completely digested in the small intestine (apparent digestibility, 98.3 and 98.3%, respectively but a fraction of the dietary fructose escaped to the large intestine (adjusted value, 11.7%). There was no carbohydrate in rectal contents of the pigs. There was no carbohydrate influence on the pre-caecal or total digestibility of nitrogen.

Bestimmung der Bakterien-N-Anteile im Kot und unterschiedlich gewonnenem Ileumchymus von Schweinen

In faeces and ileal digesta samples of 31 intact (INT) as well as 73 surgically differently prepared pigs bacterial fractionations and 2.6-diaminopimelic acid (DAP) estimations were carried out in order to calculate the bacterial N proportion in faeces N and digesta N after feeding various diets. Because of a high individual variability and the analytical variation width of the DAP/N-ratios no distinct influences of the fed diets could be found. The average DAP/N-values in the faeces (0.224) of INT pigs ranged in the same magnitude as in the digesta (0.0272) of ileorectostomized (IRA) pigs with open colon descendens (IRAo), where a digesta backflow is possible. Distinct lower DAP/N-ratios (0.0125 resp. 0.0043), however, were found in the digesta of pigs with ileo-caecal cannulae (IZB) or IRA pigs with closed colon (IRAg). On the base of various premises (N of the "bacterial fraction" C is only bacterial N; the DAP found in fraction A originates from intestinal bacteria adhering to feed particles) conducted calculations of the bacterial N proportions (in per cent of total N) led to the following data: Faeces of INT pigs: 43.0 ... 68.2 vs. 69.6 ... 89.0; digesta of operated pigs (except protein free diet) IRAo: 22.3 ... 57.0 vs. 46.2 ... 73.8; IZB: 17.0 ... 35.7 vs. 25.2 ... 53.6; IRAg (only 3 pigs): 23.6 vs. 24.2. The proportion of bacterial N in the digesta N of protein free fed IRAo pigs was 22.0 vs. 22.6%.

Assessment of apparent ileal lysine digestibility for use in diet formulation for the growing pig

The apparent ileal digestibility of lysine in a balanced diet comprising barley, meat and bone meal, fish meal and pollard as its protein sources, was determined with six growing pigs, using the slaughter technique. The mean apparent digestibility of lysine was 0.59. Concurrent with the digestibility study, a pig growth trial was conducted to determine the accuracy of ileal digestible lysine intake as a predictor of pig performance. Fifteen intact male pigs were allocated to five casein-based diets and eight pigs were allocated to the barley-based diet used in the ability study. Lysine was confirmed as the first-limiting amino acid in all diets and minerals, vitamins and essential fatty acids were in excess of requirements. The nitrogen source of the casein-based diets was lactic casein and synthetic amino acids and they had different gross lysine to digestible energy ratios. The 23 pigs were given fixed levels of meal over a 49 day period such that all received equal intakes of digestible energy. The pigs were then slaughtered and the total lysine contents of their carcasses were determined. Linear regressions of mean daily body weight gain and carcass lysine content against daily amounts of absorbed lysine were determined for the casein-fed pigs, with the assumption that the dietary lysine was completely absorbed. The actual performance of pigs on the barley-based diet was compared with that predicted using the regression equations, based on the determined (digestibility study) levels of barley-diet lysine absorbed daily. Predicted and mean actual (± SE) growth rates for the barley-fed pigs were 550 g day −1 and 509 (± 30.24) g day −1, respectively, while predicted and mean actual (± SE) carcass lysine contents were 403 g and 325 (± 25.5) g, respectively. The estimates of apparent ileal lysine digestibility overestimated the degree of lysine availability and may have overestimated the degree of lysine uptake from the gut.

The role of the large intestine in the utilization of feeds containing non-starch polysaccharides

The utilization of diets high in fibre (defined here as non-starch polysaccharide - NSP) is dependent on the extent to which the NSP is fermented by the gut microflora, and the subsequent utilization by the animal of the end-products of fermentation - the VFAs. It has frequently been assumed that fermentation of NSP in the pig occurs almost exclusively in the hind-gut. However, a number of studies using pigs fitted with ileal-cannulas have suggested that some fermentation of NSP may occur prior to the hind-gut (e.g. Graham et al., 1985). The aim of this study was to determine the relative roles of the small and large intestine in a) the digestion of feeds containing non-starch polysaccharides, and b) the subsequent utilization of energy by growing pigs. This was achieved by comparing the abilities of intact or ileo-rectomised pigs to digest and grow on cereal-based diets containing 0 or 300 g/kg sugar beet pulp.

Präzäkale Protein- und Aminosäurenverdaulichkeit sowie Gesamt-Rohnährstoffverdaulichkeit der Extraktionsschrote von drei Raps-Varietäten, ermittelt an ileorektostomierten bzw. intakten Schweinen

The apparent precaecal crude protein digestibility and amino acid absorption as well as the total digestibility of the nutrients organic matter, crude protein, crude fat and crude carbohydrates were determined of rations consisting of barley plus oilmeals of two rapeseed varieties of double quality (DQ) from Canada (Canola) and the GDR as well as of one variety of single quality (SQ) with 10 female pigs weighing between 120 and 140 kg with ileorectal anastomoses (IRA) and 4 intact (INT) female pigs weighing between 150 and 160 kg. The three rapeseed meals (RSM) were furthermore fed to IRA pigs as sole protein source together with protein-free feed. Based on the digestibilities of the crude nutrients determined with INT pigs and calculated with the difference method the energy content of RSM DQ "Canola", DQ GDR and SQ GDR could be calculated as 495, 633 and 500 EFUpig/kg DM (average: 543 EFUpig). The precaecal digestibility of the crude protein of the above mentioned RSM sorts determined with IRA pigs and calculated with the difference method amounts to 73, 76 and 75% resp. and is thus lower than the average absorption of all amino acids. The precaecal digestibilities of crude protein and essential amino acids for the mixtures calculated from the digestibility values of the individual feedstuffs barley and the above mentioned RSM largely agree with the experimentally determined digestibility values, i.e. there is additivity. On an average of the values known from literature for DQ RSM (including our own results), the precaecal digestibility of crude protein amounts to 70, of lysine to 74, of methionine to 82, of cystine to 82, of threonine to 69, of tryptophan to 72 and of isoleucine to 74%.

Untersuchungen zur energetischen Verwertung von Rationen mit Trockenkonzentraten, Kartoffeln, Zuckerrüben, Apfelpektin und Rohrzucker durch wachsende intakte und ileorektostomierte Schweine

Results of the measuring of the total metabolism of growing intact pigs (INT) and pigs with ileorectal anastomoses (IRA) are compared. The 16 comparisons are based on studies with rations of dried feedstuffs and rations containing between 30 and 50% of the DM raw or steamed potatoes and sugar beets, sucrose and apple pectin. On an average of all comparisons the relative values for the digestibility of energy, DM and the organic matter as well as for the metabolizability of the energy were between 81 and 82% (values measured at INT animals = 100). The comparison also refers to the crude nutrients, the water-soluble carbohydrates, the starch and the pectin. As a tendency, the IRA utilized the metabolizable energy better than the INT animals. The energy maintenance requirement of the IRA animals was--by 15%--significantly higher than that of the INT animals. There is not yet an answer to the question in how far comparative studies of INT and IRA animals make verified statements with regard to the differences in the energetic utilization of the precaecally and postileally digested nutrients possible. For this, further experiments will be necessary.

The Effect of Unilateral Nephrectomy on the Subsequent Radiation Response of the Pig Kidney

The left kidney of 14 Large White female pigs, approximately 14 weeks of age, was surgically removed. Thirty weeks after unilateral nephrectomy (UN) the remaining kidney was irradiated with a single dose of between 11.9 and 15.6 Gy of 60Co gamma-rays; three pigs received sham irradiation. Following irradiation glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and haematocrit (Hct) were determined for up to 48 weeks after irradiation. Irradiation resulted in a dose-dependent decline in GFR, evident 8 weeks after irradiation. This was followed by a gradual improvement in GFR, although after doses of 14.0 Gy GFR remained below control values throughout the study. A similar pattern of response was seen in terms of ERPF, but this was not dose-related. Doses of greater than or equal to 14.0 Gy also caused a significant reduction (p less than 0.001) in Hct within 4-8 weeks. Minimal levels were evident 16 weeks after irradiation; Hct then increased, but remained below preirradiation values. Dose-effect curves were obtained by determining the percentage of irradiated kidneys which showed a greater than or equal to 50% reduction in GFR and ERPF, fitted by probit analysis, and ED50 values (+/- SE) were calculated for each parameter. The ED50 values for GFR and ERPF were 14.49 +/- 0.27 Gy and 12.56 +/- 0.98 Gy, respectively. These values were not significantly different from those obtained from intact age-matched pigs in which the right kidney alone was irradiated; UN did not compromise or alter the radiation response of the kidney to irradiation. However, the ED50 values obtained for the UN pigs were significantly greater (p less than 0.001) than the values of 9.76 +/- 0.17 Gy and 6.19 +/- 0.93 Gy, seen for GFR and ERPF in intact age-matched pigs in which both kidneys were irradiated. Thus although both experimental situations involved irradiating the entire renal tissue, the relative radiosensitivity of the kidneys varied considerably. These findings show that the radiosensitivity of the pig kidney can vary markedly, depending on the physiological status of the kidney at the time of irradiation.

Stress-induced injury of pig myocardium is accompanied by increased lipid peroxidation and depletion of mitochondrial ATP

The aim of the study was to investigate the mechanisms of myocardial lesions induced by stress in conscious, intact pigs. The animals were subjected to 24 h immobilization, controls were kept in normal conditions. The pigs were killed by electric shock and exsanguination. Lipid peroxidation products: malondialdehyde (MDA), conjugated dienes (CDB), fluorescent end products (RF) and adenine nucleotides (ATP, ADP) were measured in the left ventricular myocardium which was also subjected to histoenzymatic and electron microscopic examination. In stressed animals as opposed to the control group, alterations in ultrastructure and diminution of mitochondrial ATP have been found, together with augmented formation of MDA and CDB reflecting increased free radical generation. These changes may be the component of stress-induced myocardial injury.

Decreases in repetitive extrasystole threshold in the conscious pig with myocardial infarct were reversed by tyrosine

Reports indicate that the administration of tyrosine, the precursor amino acid for catecholaminergic neurotransmitters, may be beneficial under conditions of physiologic stress. We studied the effects of tyrosine on vulnerability to ventricular arrhythmia in conscious pigs with healing myocardial infarcts, and sham operated (intact) pigs. Mean arterial pressure and heart rate were measured via chronically implanted aortic catheters. The repetitive extrasystole threshold (defined as the energy in milliamperes (ma) needed to cause a spontaneous ventricular beat following a premature beat induced by an electrical impulse), was measured via a bipolar pacing catheter placed during instrumentation surgery in the apex of the right ventricle. One week after infarct, the myocardial infarct group was studied before and ninety minutes after the administration of tyrosine (8 mg/kg iv). Before tyrosine, the myocardial infarct group had a significantly lower repetitive extrasystole threshold (12±1 ma) compared to the intact group (19±2 ma). Ninety minutes after tyrosine, the repetitive extrasystole threshold in the myocardial infarct group was 17±1 ma. The availability of tyrosine did not alter the repetitive extrasystole threshold in the intact group. Thus, vulnerability to ventricular arrhythmia was enhanced in pigs with recent myocardial infarction. Tyrosine, which can be nutritionally manipulated, may reduce myocardial vulnerability to arrhythmia after infarct.

Comparison of androst-16-ene steroid levels determined by a colorimetric assay with boar taint estimated by a trained sensory panel.

A group of 17 intact male pigs and 3 gilts ranging in weight from 96 to 260 kg was selected for sensory evaluation of boar taint in loin chops. Samples were evaluated by 10 trained judges using a 10-cm graphic scale for rating off-aroma, off-flavor, pork flavor, softness, tenderness, juiciness, and residual tissue. In addition, a fry test for taint was conducted by four experienced testers on fat samples from all animals. Androst-16-ene steroid levels were measured in salivary gland and fat. Two versions of a colorimetric assay for the androst-16-ene steroids were used, a complete version, in which cholesterol was removed from the tissue extracts using a digitonin-Sepharose affinity column, and a simplified version, which does not include this step. The off-aroma and off-flavor sensory scores showed a good correlation with the androst-16-ene levels in fat and salivary glands and high correlations were obtained between the androst-16-ene steroid levels in fat and salivary glands. The levels of the androst-16-ene steroids in the salivary gland were highly correlated with the levels of estrogen in the blood and to a lesser extent with the levels of testosterone in the blood. Similar correlation coefficients were obtained between salivary gland androst-16-ene steroid levels measured using either the complete or simplified versions of the colorimetric assay and the off-aroma and off-flavor sensory scores. The results of the fry test were variable and no statistically significant correlations were obtained between the fry test results and the off-aroma and off-flavor sensory scores from the trained sensory panel.(ABSTRACT TRUNCATED AT 250 WORDS)

Isoflurane and Halothane Attenuate Coronary Artery Constriction Evoked by Serotonin in Isolated Porcine Vessels and in Intact Pigs

Serotonin is a vasoconstrictor thought to cause coronary artery constriction in humans. The purpose of this study was to determine if isoflurane and halothane each attenuated coronary artery constriction evoked by serotonin in pigs. Both in vitro and in vivo experimental methods were used. Isolated coronary arteries with an without endothelium were studied in organ chambers in the presence and absence of 2.5% concentrations of the anesthetics. In intact pigs serotonin was infused directly into the left anterior descending coronary arteries to induce constriction. The vasodilator effects of 0.5%, 1.25%, and 2.0% isoflurane and halothane were determined using quantitative angiography. Contractile responses of isolated coronary arteries were depressed by the two anesthetics. Maximum contractile responses to serotonin were as follows: rings with endothelium 45 +/- 5% untreated versus 29 +/- 5% with isoflurane 2.5% (difference between dose-response curves, P less than 0.01) and without endothelium 67 +/- 5% untreated versus 51 +/- 6% with isoflurane 2.5% (P less than 0.001); with endothelium 52 +/- 7% untreated versus 28 +/- 7% with halothane 2.5% (P less than 0.001) and without endothelium 65 +/- 5% untreated versus 40 +/- 6% with halothane 2.5% (P less than 0.001). In intact pigs isoflurane and halothane dilated constricted coronary arteries with and without endothelium at all anesthetic concentrations tested, including concentrations as low as 0.5%. Isoflurane 1.25% increased diameter of vessels with endothelium from 1.5 +/- 0.1 mm to 1.7 +/- 0.1 mm (P less than 0.02) and halothane 1.25% increased diameter from 1.6 +/- 0.1 mm to 1.7 +/- 0.1 mm (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Bromocriptine-induced reduction of body fat in pigs

An experiment was conducted with 36 crossbred finishing pigs (18 male castrates and 18 females) to evaluate the effect of bromocriptine implants on growth, feed intake, feed efficiency, plasma urea nitrogen (PUN) and carcass characteristics. Three levels of bromocriptine (0, 5 and 10 mg/[pig.d]) were administered, via implants at the base of the ear, to six (two replicates of three) male castrates or to six (two replicates of three) intact female pigs (2 x 3 factorial arrangement of treatments). Average initial weight of pigs at the time of implantation was 89.7 kg, and the implants remained in the pigs for 28 (replicate 1) or 30 (replicate 2) d prior to slaughter. Gain, feed intake and efficiency of feed utilization were not affected (P greater than .10) by bromocriptine. Plasma urea nitrogen was lower in female pigs administered 10 mg bromocriptine; bromocriptine did not affect PUN of male pigs (gender x bromocriptine, P less than .08). Tenth rib fat thickness and average backfat thickness were lower (P less than .06) and percentage of muscling was higher (P less than .06) in pigs implanted with bromocriptine. Female pigs had less 10th rib fat but larger loin eye areas and a greater percentage of muscling than male pigs.

Fentanyl Is Devoid of Major Effects on Coronary Vasoreactivity and Myocardial Metabolism in Experimental Animals

Experiments were designed to determine the effects of fentanyl on coronary vascular tone and energetic state of the heart. Both arterial and arteriolar responses were assessed; particular attention was directed to epicardial vessels. Four experimental methods and three animal species were used. Isolated canine coronary artery rings with and without endothelium were suspended in organ chambers, and changes in their tension were measured. Fentanyl (100 ng/ml) had no effect on resting tension of unstimulated rings on a contraction evoked by serotonin 10(-8) to 10(-4) M. In rings with endothelium, the opioid had a minimal depressant effect on the contractile response to phenylephrine. Tension of vessels precontracted with serotonin (3 x 10(-7) M), or phenylephrine (10(-5) M) was unchanged following fentanyl at 10, 30, 70, or 150 ng/ml. Computerized quantitative angiography was used in intact pigs anesthetized with ketamine to determine the effects of fentanyl on coronary artery diameters of vessels with or without endothelium. Intravenous fentanyl 50 and 250 micrograms/kg had no effect on vessel diameters. Isolated perfused rat hearts were used to assess fentanyl effects upon coronary flow and arteriolar tone and upon myocardial energy state. Coronary blood flow was not altered by fentanyl (100 ng/ml) and was unchanged following washout of the drug. The heart maintained a normal energy status prior to and following fentanyl treatment. These data demonstrate that, under the conditions tested, fentanyl is devoid of major effects on the coronary circulation and upon myocardial metabolism.

Interaction of dietary protein content and exogenous porcine growth hormone administration on protein and lipid accretion rates in growing pigs.

Sixty-six intact male pigs were used to investigate the relationships between exogenous porcine growth (pGH) administration (0, excipient-treated, and .09 mg recombinant pGH.kg-1.d-1) and dietary protein content (8.3, 11.4, 14.5, 17.6, 20.7 and 23.8%) on protein and lipid accretion rates over the live weight range of 30 to 60 kg. Feed intakes were restricted (1.84 kg.pig-1.d-1) and pGH was administered daily by i.m. injection. Rate of protein deposition increased with increasing dietary protein up to 17.6 and 20.7%, respectively, for control and pGH-treated pigs; both growth and protein deposition were enhanced by pGH on the four higher protein diets but remained unaffected by pGH administration to pigs given the two lowest protein diets. Plasma IGF-I concentration was elevated by pGH administration in pigs given the four higher protein diets but unaffected by pGH with the two lowest protein diets. Rate of fat deposition was depressed on all dietary protein treatments by pGH administration; carcass fat content of control and pGH-treated pigs declined with each increase in dietary protein up to 17.6 and 23.8%, respectively. The results demonstrate that pGH acts independently on protein and lipid metabolism.

Progestins affect reproductive behavior and androgen receptor dynamics in male guinea pig brain

The present study extends previous studies of ours by comparing the anti-androgenic effect of a progestin agonist (R5020) with progesterone (P). Intact male guinea pigs treated with P (1 and 10 mg/day) and R5020 (100 μg/day) had greater latency to mount and lower numbers of mounts and intromissions compared to controls. Ejaculation and plasma testosterone concentration were not affected. Specific brain regions were analyzed for androgen receptor (AR) content. Progestins produced fewer ( P < 0.01) nuclear AR in hypothalamus-preoptic area and pituitary without associated changes in cytosolic AR. These data are best interpreted by postulating an effect of P and AR dynamics mediated through the P receptor and not by competition for androgen binding to its receptor.

A note on the live-weight growth in indigenous nigerian pigs

Live-weight growth was studied for 64 female, 64 castrated male and 64 intact male indigenous Nigerian pigs at 16 ages from birth to 672 days. The weights obtained were fitted into four different growth functions to derive prediction equations for the models used. The quadratic (W = a + bt + ct2) and the Schmalhausen functions (W = at) described live-weight growth better than the simple linear function fW = a + bt). Estimating live-weight growth using Brody's function (Y = aebt) gave the least exact predictive ability. Linear growth in indigenous Nigerian pigs occurred between 112 and 336 days. Castrated male pigs exhibited higher live-weight growth rates than either the female or intact male pigs. Differences in the prediction of live weights using the four growth functions and the actual live weights are presented and discussed.

Myocardial creatine kinase exchange rates and 31P NMR relaxation rates in intact pigs.

In this study, we used 31P NMR to investigate the relationship between cardiac workload and creatine kinase flux in intact pigs. NMR measurements were performed on anesthetized miniature swine in which a surface coil was surgically implanted on the surface of the left ventricle. Cardiac workload was varied by infusion of norepinephrine. Phosphate exchange between creatine phosphate and ATP was measured by a combined saturation transfer, saturation recovery pulse sequence. Exchange measurements showed that creatine kinase flux and concentrations of PCr and ATP were independent of workload for a 2.5-fold range of cardiac rate-pressure products. It appears that, if creatine kinase flux is coupled to work load, the pig heart operates in a regime where small changes in metabolite concentrations or creatine kinase flux are sufficient to maintain elevated workloads. Exchange and relaxation measurements, at 2.0 and 4.7 T, yielded T1 relaxation times for creatine phosphate and ATP which are longer than most reported values. Analysis of the T1 data indicates that chemical-shift anisotropy is a plausible mechanism for a portion of the spin-lattice relaxation rate at high field strengths.