Effects of human chorionic gonadotrophin on contractile activity of steroid-primed pig myometrium in vitro.

We examined the effects of (a) oestrogen and progesterone on concentrations of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in uterine smooth muscle in vivo and (b) hCG on spontaneous myometrial contractions in vitro. Ovariectomized gilts received 2 ml corn oil (control; n = 5), 2 mg oestradiol benzoate (n = 6) or 20 mg progesterone (n = 5) for 5 days. Gilts were hysterectomized 8 h after the last injection and longitudinal sections of myometrium were incubated in modified Krebs' solution with 0 or 10 i.u. of hCG (n = 10/gilt) for 4 h at 37 degrees C in 95% O2:5% CO2. After incubation, myometrial sections were placed in a tissue chamber perfused with Krebs' solution and mechanical activity was recorded for 30 min. Cell membrane fractions were prepared from myometrial tissue not used for in-vitro studies and analysed for LH/hCG receptors. Treatment with oestradiol benzoate increased (P less than 0.01) the number of LH/hCG-binding sites compared with gilts receiving corn oil or progesterone. Incubation of myometrium with hCG reduced (P less than 0.01) the frequency and amplitude of spontaneous uterine contractions in gilts treated with oestradiol benzoate. In contrast, hCG had no effect (P greater than 0.05) on the pattern of myometrial contractions in gilts given corn oil or progesterone. These results indicate that oestradiol promotes the synthesis of LH/hCG receptors in pig myometrium and incubation of oestrogen-primed tissue with hCG has a quiescent effect on myometrial contractility.

The effect of age on the rhythmic contractions of the rat small intestine.

In vivo and in vitro rates of intestinal rhythmic contractions were measured in the same rats varying in age from very young to the senescent. Two rat strains, three small intestine locations, and six ages were compared. Contraction rates determined in vivo and in vitro were similar. Rhythmic contractions at all ages were fasted in the duodenum, slower in the jejunum, and slowest in the ileum. Contractions at 10 days of age were significantly slower than at all other ages; otherwise no systematic age-associated difference in contractions was demonstrated in either strain. Several factors were suggested as possibly influencing the developmental aspects of contraction rate and, therefore, their potential involvement in the early post natal period was suggested. It appears that old age does not influence the rate at which rhythmic contractions occur in the small intestine of the rat, and very possibly, these results are applicable to other species including humans.

Milk temperature in the claw piece of the milking machine and mammary surface temperature are predictors of internal mammary temperature in goats.

Mammary internal and surface temperatures and milk temperature were correlated using five lactating goats. Internal mammary temperature was estimated using temperature-sensitive transmitters placed deep within the parenchyma of each mammary half. External mammary temperature was estimated using infrared thermography of four mammary skin sites: T1, teat end; T2, teat base; G1, about 20 mm above the teat base; and G2, about 20 mm ventral to the base of the gland deep to the thigh. The thermistor bead used for estimating milk temperature was placed in the claw piece where the short milk tube of the liner attaches. This placement minimized cooling effects of milk contact surfaces. The overall correlations of milk temperature with mammary temperatures ranged from 0.45 to 0.64. Correlations among the six paired values for the four external sites ranged from 0.76 to 0.92. Milk and surface temperatures, milking time, and milk weight were employed in various combinations as covariables; these were calculated within animal, within half. Milk temperature was the single most important predictor of internal mammary temperature in all models. Milk temperature alone or combined with covariables can be used to predict internal mammary temperature.

Effects of rapid weight gain to puberty on reproduction, mammary development and lactation in ewe lambs.

The effects of rapid weight gain to puberty on reproduction, mammary development and milk production in ewes lambing at 13 mo of age were investigated on three trials. A total of 64 Dorset and 93 Suffolk ewe lambs were weaned at 42 d of age and their mean weight was 16 kg. These ewes were assigned, within breed groups, to either a finishing diet or a growing diet. Onset of puberty was determined by daily checks for estrus and ewes were bred beginning at 7 mo of age. In Trial 2, mammary gland development was determined in eight Suffolk ewes from each diet. Ewes on the finishing diet were younger at puberty than those on the growing diet (199 vs 206 d, P<0.05) but required more services per conception (1.3 vs 1.1, P<0.05). Dietary conception rate and lambing rate means were similar. Mean 4-h milk yield was lower (P<0.10) for ewes on the finishing diet (283 g) than for those on the growing diet (310 g). Mammary gland fat pad area was higher (P<0.05) for ewes on the finishing diet compared with those fed for growth. Gross and adjusted duct areas were higher in ewes on the growing diet, but differences were not significant. At puberty, negative correlation coefficients for milk yield with performance traits were as follows: daily weight gain, -0.184 (P<0.08); weight-to-height ratio -0.262 (P<0.01); body condition score, -0.189 (P<0.07); and body weight, -0.212 (P<0.05). Results of this study indicate that rapid weight gain to puberty impairs mammary gland development and milk production in ewe lambs.

A method for silver impregnation of mammary myoepithelia.

Histochemical methods for microscopic visualization of mammary myoepithelial cells all yielded considerable variation in completeness of myoepithelial cell staining. Although extremely variable, silver impregnation occasionally gave tissue sections containing myoepithelia having excellent microanatomical detail and contrast with other tissue elements. Consequently, sources of variation in the silver technique were considered. Composition of the tissue fixative and pH of the silver impregnating solution were most critical. A final method is presented which gives consistent, complete silver impregnation of myoepithelia, where both the cell body and cell processes are clearly evident. The staining procedure is not light sensitive, nor is acid cleaning of glassware necessary. Tissue sections from lactating mouse, rat, hamster and goat are presented; tissue from other species should stain as well. The procedure should greatly facilitate the study of the function of myoepithelial cells and the visualization of these cells in mammary pathology.

Effects of accelerated growth during rearing on reproduction and lactation in ewes lambing at 13 to 15 months of age.

Three trials were conducted using ewe lambs to determine the effects of accelerated growth during rearing on reproduction and lactation. Data were obtained on 113 ewes. Early weaned ewe lambs were randomly assigned to the following prebreeding treatments: (1) thin (T, moderate gain) and (2) fat (F, accelerated gain). They were bred to lamb at 13 to 15 months of age. After breeding, one half of the ewes on the T and F treatments were switched to the other treatment so that postbreeding treatments were TT, TF, FF and FT. Prebreeding treatment did not affect conception rate (T, 95%; F, 96%), but lambing rates were 43, 28 and 27% higher (P<0.05) for F than T ewes in trials 1, 2 and 3, respectively. Daily milk production was higher in T ewes than F ewes for each trial, but the differences were significant only in trial 3. Estimated daily milk yields over the 60-day period were: T ewes, 1482, 1571, 1614 g; F ewes, 1183, 1373, 1321 g for trials 1, 2 and 3, respectively. Number of alveoli also favored T ewes. Switching ewes to the alternate treatment after breeding did not affect reproduction or milk production. Correlations between weight to height ratio and milk yield were negative in trials 1 and 3 but were positive in trial 2. There was no indication that serum T(4) levels affected milk production or reproduction. The results of this study show that accelerated growth during rearing increased lambing rate but may impair milk production. These effects appeared to be fixed by the time the ewes were bred.

Scanning electron microscope visualization of the mammary gland secretory unit and of myoepithelial cells.

Mammary gland pieces from lactating mice were incubated for various times up to 4 h in collagenase and then additionally for up to 1.5 h in a mixture of collagenase and hyaluronidase. Tissue then was fixed and prepared for scanning electron microscope viewing. Monitoring of time of enzymic hydrolysis allowed visualization of connective tissue sheets, secretory lobules, blood vessels, alveoli encased in and devoid of basement membrane, secretory epithelia, alveolar milk ducts, and myoepithelial cells. Scanning electron microscope viewing of alveoli in cross section showed good internal micro-anatomy including a valve-like arrangement of secretory epithelia at the point of milk duct attachment. Morphology of myoepithelial cells and their relationship to secretory cells and to each other was presented. There was no evidence that myoepithelial cells were interconnected continuously throughout the tissue, but they interlaced over an alveolus; thus, the concept of a limited physiological syncytium was advanced.

Effects of pregastric esterase on utilization of whole milk by preruminant calves.

The role of pregastric esterase was investigated in four abomasally-cannulated calves during a sequence of ten 3-day periods beginning when calves were 2 to 5 days of age. Two calves were fed whole milk from nipple bottles to maximize exposure to pregastric esterases, and two other calves were given milk by infusion directly into the abomasum to minimize exposure. The initial system of feeding each calf was continued for eight periods after which treatments were reversed. Postfeeding lipolytic activity of samples of abomasal contents and of intragastric lipolysis of milk fat were markedly greater for orally-fed calves than for abomasally-fed. Systems of feeding effected no significant differences in a) digestibility of dry matter, fat, crude protein, and nitrogen-free extract, b) retention of nitrogen, and c) percentage weight gains. Digestibility of dry matter, crude protein, and nitrogen-free extract of milk and retention of nitrogen were greater in later periods than in initial. Although age of calves was a positive factor associated with utilization of milk, decreased exposure of milk to pregastric esterase and the resulting reduction of lipolysis in the abomasum did not effect a detectable lowering of milk utilization by calves in age groups studied.