1. Three experiments were conducted using Lotus pedunculatus containing high concentrations of condensed tannins (CT), and utilizing the principle that polyethylene glycol (PEG) application (molecular weight 3350) will irreversibly bind a portion of the CT and thus reduce the dietary reactive (i.e. non-PEG bound) CT concentration. Lotus diets containing 95, 45 and 14 g total reactive CT/kg dry matter (DM), induced by spraying with three PEG rates, were given to sheep at hourly intervals (600 g DM/d) for 21 d (Expt 1). In Expts 2 and 3, lambs grazed areas oversown with either lotus (89 g CT/kg DM) or clovers (Trifolium repens and Trifolium pratense; < 1 g CT/kg DM) for 42 and 92 d respectively. In Expt 2 half the animals grazing each forage received oral PEG (75 g/d), whilst in Expt 3 half the lambs were sired by rams selected respectively for low or high levels of subcutaneous fat deposition.2. Hormone concentrations in plasma (Expt 1 only) were determined by radioimmunoassay. Rates of [U-14C]-acetate and ~-[U-~~C]glucose incorporation and oxidation by subcutaneous and abdominal adipose tissue removed at slaughter, together with rate of glycerol release, were determined during in vitro incubation in all three experiments.3. Plasma concentration of growth hormone was positively and linearly related to dietary reactive CT concentration, whilst 3,5,3'-triiodothyronine (T,) concentration tended to be negatively and linearly related to dietary reactive CT concentration. Diet CT concentration had no effect on plasma concentrations of the other hormones measured.4. Feeding of lotus high in CT was associated with a consistent but non-significant increase in the rate of glycerol release from adipose tissue, which was reduced as dietary reactive CT concentration was lowered through PEG application, and a reduction in the lipogenesis: lipolysis value. Selection for leanness decreased acetate incorporation and increased glycerol release from adipose tissue, with the effect not interacting with the diet.When tissues of Lotus sp. or sainfoin (Onobrychis viciifolia Scop) plants are disintegrated, such as during chewing, condensed tannins (CT) present in certain specialized cells are known to precipitate the soluble plant proteins by pH-reversible hydrogen bonding (Jones & Mangan, 1977). This action of CT, present in the leaves and stems of these two species, but not in those of white clover (Trifolium repens), red clover (Trifolium pratense) or lucerne (Medicago sativa), is known to increase non-ammonia-nitrogen (NAN) absorption from the intestines (Barry & Manley, 1984; Barry et al. 1986). The presence of CT has also been accompanied by increases in N retention in sheep, both for diets of sainfoin (Egan & Ulyatt, 1980), Lotus corniculatus (John & Lancashire, 1981) and Lotus pedunculatus (Barry et al. 1986). The presence of CT in Lotus pedunculatus has also been associated with reduced carcass fat content in grazing lambs, relative to lambs grazing white clover (Purchas & Keogh, 1984). The objectives of the present work were ...

Plasma ACTH, arginine vasopressin (AVP), and catecholamines were measured at 5-min intervals in the pituitary venous effluent of the unanesthetized horse. Pulses of ACTH and AVP were found to be surprisingly brief (usually of less than 10-min duration) and frequent (averaging between 15-25 min). A highly significant relationship in the changes in concentration of these two hormones was demonstrated (P less than 0.0002) both at rest and after a mild hypoglycemic stimulus. Although there was also a significant correlation (P less than 0.005) between simultaneous plasma ACTH and AVP values the pulse amplitude ratio of AVP to ACTH showed a considerable variation. A rise in cortisol appeared to have a greater suppressive effect on the amplitude of ACTH than AVP pulses. The gradient in hormonal concentration between pituitary effluent and jugular plasma was at times over 50-fold for ACTH, and 500-fold for AVP. A gradient was also found for epinephrine, norepinephrine, and dopamine. A highly significant correlation (P less than 0.005) was demonstrated between changes in norepinephrine, ACTH, and AVP concentrations, but no such relationship could be shown for epinephrine and dopamine. It is concluded that there is a close temporal relationship between changes in ACTH, AVP, and norepinephrine concentrations. Pulses of these hormones are greater in amplitude and more frequent than would have been suspected from sampling peripheral plasma. The variability in the pulse amplitude ratio of ACTH and AVP may suggest that other factors are affecting ACTH secretion. The ability to sample frequently for several hormones and to obtain a marked gradient in hormonal secretion between the pituitary venous effluent and jugular plasma suggest that the horse should provide an excellent animal model in which to study the regulation of hypothalamic and pituitary hormone secretion.

Plasma ACTH, arginine vasopressin (AVP), and alpha MSH were measured in pituitary venous effluent at 5-min intervals from five unanesthetized horses during cortisol infusion and after an iv bolus of AVP or ovine (o) CRF. In control experiments (no hormone) there was a significant overall correlation between the timing of concentration changes in ACTH and alpha MSH. Cortisol infusion increased jugular cortisol levels by 70% and was associated with a reduction in mean ACTH, AVP, and alpha MSH secretion rates and ACTH peak secretion rate, but did not alter the observed pulse frequencies of these hormones. Administration of AVP raised plasma concentrations to a level comparable to the spontaneous peaks in pituitary venous blood and resulted in an increase in the secretion of ACTH and alpha MSH in all horses. Furthermore, spontaneous AVP peaks occurred in pituitary venous blood between 90 and 180 min after AVP injection, indicating that the exogenous hormone did not suppress AVP secretion. oCRF administration led to a prolonged elevation in plasma CRF and an increase in secretion of ACTH and alpha MSH, but not AVP, in all horses. The pulsatile secretion of ACTH and alpha MSH was maintained despite plasma CRF levels in excess of 400 pmol/liter, and the timing of concentration changes in AVP and ACTH continued to be highly correlated. It is concluded that pulsatile ACTH secretion continues during cortisol, oCRF, or AVP administration. Like that of ACTH, alpha MSH secretion is stimulated by oCRF and AVP administration and suppressed by cortisol. Although the timing of concentration changes in ACTH and alpha MSH is highly correlated, the correlation of the actual concentrations of these two hormones varies considerably in different animals.