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Search for other papers by A. L. C. WALLACE in
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SUMMARY
An electrophoretically homogeneous component obtained by starch gel electrophoresis of sheep growth hormone (GH) has been used to prepare antiserum in rabbits. By means of a haemagglutination—inhibition reaction, this antiserum was used to assay GH both in sheep pituitary extracts and in sheep sera. The values for the GH content of a number of pituitary extracts obtained by both immunological and biological assay methods were in good agreement. GH levels in sheep serum were found to range between 38 and 600 μg./100 ml.
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Search for other papers by A. L. C. WALLACE in
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The effect of thyrotrophin releasing hormone (TRH) on thyroid and pituitary function has been investigated as a possible aid to the early selection of cattle suited to tropical conditions. Two groups of six calves were used, one a shorthorn breed (SH) adapted to temperate conditions and the other an Africander cross (AX) selected for tropical climates. The dose and time responses of serum thyroid-stimulating hormone (TSH), tri-iodothyronine (T3), thyroxine (T4) and prolactin to single, repeated or multiple doses of TRH were measured by radioimmunoassay.
Levels of T3 and T4 before injection were lower in the SH than in the AX calves. After a single injection of TRH (0·4, 1, 2·5 or 5 μg/kg live weight) the percentage increase in T3 in the AX group was significantly lower than that in the SH group. No relationship was observed between the various doses and the magnitude of the response. There was, however, a negative correlation between values of T3 before injection and the maximum T3 response. The T4 : T3 molar ratio was also significantly lowered between 2·5 and 4·5 h after injection of TRH.
Changes in prolactin but not TSH concentrations were dependent upon the breed. After TRH injection, the initial increase in prolactin concentration was the same in both breeds but in the AX group the concentration then declined to values well below the pre-injection concentrations. In the SH group the prolactin concentrations returned to pre-injection levels.
When TRH was injected on 2 successive days the T3, T4 and TSH responses were less on the second day in both breeds. The prolactin response differed between breeds in a similar manner to that following a single injection of TRH.
Repeated hourly injections of increasing amounts of TRH for 4 h resulted in maximal increases of TSH after 2 h and of prolactin after 1 h. Despite continued injection the concentration of both hormones declined.
In the AX breed T3 and T4 concentrations continued to increase for 8 h after the first TRH injection whereas in the SH group no further increase in the concentrations of these hormones occurred after the first 4 h.
It is concluded that the information obtained by measuring resting serum T3 and T4 concentrations combined with changes in T3 and prolactin concentrations after TRH injection may aid in the early selection of cattle adapted to tropical conditions.
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Search for other papers by K. A. FERGUSON in
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SUMMARY
The distribution, potency and yield of growth hormone (GH), prolactin, thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH) and luteinizing hormone (LH) activities and the electrophoretic behaviour on starch gel have been studied in fractions obtained by chromatography on DEAE-cellulose of pituitary extracts from man, sheep, ox, pig and whale.
In none of the species examined was the distribution of hormonal activities identical. GH, TSH and FSH in the sheep and ox, and GH and LH in the pig and whale, appeared in corresponding fractions. The prolactin activities from the five species were found in closely similar elution volumes. The hormonal activities of the human extract occurred over a much smaller range of distribution volumes than those of the other species. The GH fractions from all five species and the prolactins from sheep and ox were relatively potent preparations.
Starch gel electrophoresis showed a number of components in all fractions. The distribution of components in corresponding fractions was different for each species, although some components had similar mobilities.
These results add to the growing evidence of the species-specific nature of pituitary hormones and to the information available for evolving comprehensive fractionation systems for each species.
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Search for other papers by A. L. C. WALLACE in
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The injection of oestradiol benzoate (OB) into the ovariectomized ewe induced a biphasic response in circulating luteinizing hormone (LH). There was a fall in concentration during the first 8–12 h after injection, and then a rapid increase in concentration during the next 12 h. Sodium pentobarbitone anaesthesia, begun either at the time of injection of OB, or 8 or 16 h later, did not affect the first phase, but prevented the second phase of this response. The injection of synthetic luteinizing hormone releasing factor caused a release of LH that was similar both in anaesthetized and conscious ewes. The results indicated a non-nervous site for the inhibitory action of oestrogen on circulating LH, and a central nervous site of action of oestrogen in stimulating LH release.
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Search for other papers by A. L. C. WALLACE in
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Several methods are now available for the immunoassay of insulin in plasma. Of these, the double antibody technique of Hales & Randle (1963) is especially convenient. However, in studies of plasma insulin concentrations in the sheep with method C of Hales & Randle (1963), plasma samples assayed undiluted consistently yielded higher values than the same plasma samples assayed after 1:4 dilution with buffer B of Hales & Randle (1963). Addition of ovine insulin (0–200μ-u./ml.) to ovine plasma showed that the sensitivity of the assay was greater in undiluted plasma than in buffer, the decrease in antibody-bound labelled insulin for a given increment in insulin concentration being greater in the plasma system. Addition of 0·01 m-EDTA (Morgan, Sorenson & Lazarow, 1964; Sheldon & Taylor, 1965) did not eliminate this discrepancy. Insulin standards in buffer did not appear to provide a suitable baseline for assay of insulin in undiluted ovine plasma.
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Search for other papers by W. R. SOBEY in
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SUMMARY
The NIH-B2-GH preparation of ox growth hormone (GH) was separated by chromatography on DEAE-cellulose into six fractions. Five of these fractions when assayed in hypophysectomized rats showed GH activity ranging in potency from 0·25 to 2·5 times the starting material. Growth activity could not be correlated with the concentration of any single component revealed by starch gel electrophoresis.
Antisera produced to NIH-B2-GH had antihormone activity and produced two precipitin lines in Ouchterlony diffusion tests. One of these lines was associated with serum γ-globulin and was shared by all five fractions. The other line was present in only two of the fractions, and these contained the more anionic components.
It is suggested that the more cationic growth-active components present in bovine and ovine GH preparations do not readily produce precipitating antibodies and that this may complicate the results of precipitin and gel diffusion tests when heterogeneous GH preparations have been used to prepare the antisera.
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Search for other papers by A. L. C. WALLACE in
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SUMMARY
The entry of 125I-labelled ovine follicle-stimulating hormone (FSH) and human serum albumin into the seminiferous tubules of rams has been studied by measuring radioactivity in blood plasma and rete testis fluid after an intravenous injection of the labelled protein. After the injection of FSH, radioactivity/mg total protein in rete testis fluid exceeded that in blood plasma from the first day onwards, but after the injection of human serum albumin, radioactivity/mg total protein in rete testis fluid only reached that in plasma after 4–5 days and never exceeded it. Protein-bound radioactivity disappeared from the blood more quickly after an injection of FSH than after an injection of albumin.
The volume of distribution for ovine FSH in the testes of rats was greater than that for human serum albumin. The volume of distribution for FSH was greater, in absolute terms, in the testes with the efferent ducts ligated 24 h previously than in the contralateral control testes when the FSH was injected at the time of efferent duct ligation. The volume of distribution for albumin was slightly less in the ligated testes than in the control testes. This suggests that FSH but not albumin had penetrated into the fluid trapped inside the testis. The liver and kidney had much higher concentrations of protein-bound radioactivity per unit weight than did the testis after the injection of FSH, so it does not seem that FSH is selectively taken up by the testis.
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Search for other papers by J. M. BASSETT in
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SUMMARY
Plasma growth hormone (GH) concentrations in adult sheep and lambs were measured by radioimmunoassay. Mean values before feeding were 3·1 (s.e. − 0·4, + 0·5) ng./ml. in lactating ewes and 3·9 (− 0·5, + 0·7) ng./ml. in their lambs. In adult wethers the mean GH concentration before feeding was 2·3 (−0·2, + 0·3) ng./ml.
After one i.v. injection of 400 μg. ovine GH, the hormone disappeared from the plasma of adult sheep with a half-time of 7–8 min. Plasma GH concentrations decreased at a similar rate after the establishment of high concentrations of endogenously secreted GH. The results suggest a shorter half-life than has been reported for human GH in man. GH could not be recovered in an immunologically recognizable form in urine. Fasting for 4 days led to no systematic change in plasma GH concentrations. Feeding did not increase plasma GH. Intravenous injection of saline resulted in some increase in plasma GH in both ewes and lambs. In adult sheep intravenous glucose (0·25 g./kg.) did not cause any greater change than that seen after saline, but in lambs an increase occurred. Intravenous injection of insulin (0·25 unit/kg.) resulted in an increase in plasma GH at 15–30 min. and this effect was found in both lambs and ewes. Infusion of adrenaline at either 25 μg. or 50 μg./min. into adult wethers (average body wt 51 kg.) caused a decrease in plasma GH concentration. It was concluded that the changes in plasma GH concentration of sheep in a number of physiological situations differ from those reported to occur in man.
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Search for other papers by G. D. THORBURN in
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SUMMARY
A radioimmunoassay technique for measuring the thyrotrophin (TSH) concentration of sheep and cattle plasma is described. The sensitivity of the assay allowed the measurement of 1–50 ng TSH/ml unextracted plasma. Cross-reaction with ovine luteinizing hormone, prolactin and growth hormone was very low. The average recovery of added TSH was 103 ± 4·1 (s.e.m.)% and the between-assay coefficient of variation was 13·8%.
The normal plasma TSH levels of sheep and cattle were approximately 2·5 ng/ml (5 mu. bovine TSH/100 ml). Foetal sheep had plasma TSH concentrations of approximately 3·2 ng/ml during the last 20 days of gestation. Levels of TSH in the circulation decreased abruptly after hypophysectomy of the foetal lamb and a decline in the plasma thyroxine (T4) concentrations was also apparent within 24 h of the operation. However, thyroidectomy of adult and foetal sheep did not increase plasma TSH concentrations until almost all the T4 had been cleared from the circulation.
The injection of T4 into thyroidectomized sheep rapidly reduced plasma TSH concentrations to normal values. However, the continued injection of T4 did not further reduce TSH concentration. The injection of T4 or triiodothyronine into normal sheep was also without effect on plasma TSH concentrations.
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Search for other papers by G. D. THORBURN in
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SUMMARY
The rate of removal of immunoreactive, intravenously injected 125I-labelled sheep growth hormone (GH) was used to calculate metabolic clearance rates (MCR) in two foetal lambs at 130 days of gestation and in two 6-day-old lambs. The mean MCR calculated for the foetuses was 2·9 ml/min/kg and for the lambs 3·1 ml/min/kg. The concentration of GH in plasma sampled before injection was determined immunologically and the values were used to calculate production rates. A production rate of 924 ng GH/min was calculated for the foetuses and 85 ng GH/min for the lambs. The effect of sectioning the pituitary stalk was studied in two foetuses; after the operation there was a rapid decrease in the circulating levels of GH. Hypophysectomy in two other foetuses also caused an abrupt decrease in plasma GH concentration.
It was concluded from these experiments that the exceptionally high concentrations of GH in the plasma of foetal lambs could not be attributed to impaired removal of the hormone from the circulation. The direct cause of the increased hormone concentrations was a high rate of GH secretion resulting from active stimulation of the foetal pituitary by the hypothalamus.
