Starting in mid-lactation, goats were treated daily for 22 weeks with 0.15 mg recombinant bovine GH (bGH)/kg, or an equivalent volume of vehicle. One gland of each goat was milked thrice daily throughout treatment, the other twice daily. Mammary differentiation was studied in biopsy samples obtained before treatment and after 3 and 22 weeks of treatment, by determination of in-vitro synthesis rates of milk constituents and measurement of enzyme activities. Mammary growth was measured using a whole-body imaging technique (magnetic resonance imaging; MRI). bGH caused an immediate and sustained increase in milk yield of approximately 23% overall, whilst the glands milked thrice daily produced approximately 14% more than the control glands milked twice daily. The effects of the combined treatment were additive, but not synergistic. A synergistic effect of the combined treatment resulted in a significant improvement in lactation persistency. A stimulatory effect of milking frequency on mammary enzyme activities was evident only in bGH-treated goats at 3 weeks, but in both groups at 22 weeks. Synthesis rates of casein and lactose were increased at 3 weeks only by the combined treatment. Thus bGH accelerated or augmented the differentiative response to thrice daily milking. Mammary parenchyma volume, estimated by MRI, increased significantly during the first 12 weeks of bGH treatment and remained higher throughout the rest of the treatment period. Cell number was estimated from parenchyma volume and DNA concentration; this decreased significantly in the controls between weeks 1 and 22, but remained constant in the bGH group. In nine of the ten goats, parenchyma volume and cell number increased in the gland milked thrice daily relative to the control gland milked twice daily during the course of the experiment. Thus bGH stimulated growth of the mammary gland over and above that induced by the frequent milking. The absence of any detectable increase in thymidine incorporation suggests that this growth consisted of cellular hypertrophy rather than hyperplasia.

0 R o \ 147, Livcrpx)l, L69 3BX, UK. and 'Hannah Rescarch Institutc. Ayr. KA6 SHL, UK.In order to understand thc intercellular prtmsscs governing m a m n i q growth in the ruminant mammary gland we have examined the histology and immunophenotypic properties ot cclls in gtut mammary tissuc at different stages of development. This study cmploycd standard histochemical and immuntxyttxhemical techniques with immunological markers of ccll typcs which have previously been used in the study of rtdcnt I I I and human 121 mammary tissue.Mammary tissuc was obtained from goats at key stages 01-mammary development: virgin (6 months of age); pregnant (5 wccks pre-partum); lactaong (2nd wcck of twice daily milking); involuting (3rd week after ccssation of milking). Tissues were lixed in Mtdificd Mcthacam ((50% methanol, 30%) Inhibisol, 10% acetic acid; v h ) and prtxesscd and embedded in paraffin wax using standard histological prclcedurcs. Sections wcrc cut aid stained with haematoxylin and cosin or immunocyttxhemically s t a n d using the ABC mcthtxl (DAKO, High Wycombe, UK).The ductal stmcture in a &month cid virgin g t~t was traced and identified in scnal histological w t i o n s of mammary parenchyma. 'l'hc ductal system culminated in terminal ductallobular units (TDLU) which were comprised of lobules of blindending ducts or ductules (DTL). These DTLs wcrc connected to intmlobular terminal d u c~s that were draned by extralobular terminal ducts. The structure of the DTLs varied according to the physiological status of the gtat. In resting glands, the majority of DTLs wcrc in the form of alvetJar buds which expanded during gestation to form grape-like lobules of alveoli. In lactating glands, dilation of DTLs was at a maximum forming true sccrettw)? alvetii. All ducts and DTLs were lined by 1-3 layers of cuboidal, (or columnar in lactating glands), epithelial cells which. in turn, were surrounded by a single layer of myoepithelial cclls. The involuting gland was chardcterised by the wilapse of alvecdi causal by the loss of columnar mtwphtdogy of the alveolar cells which resulted in mytqnthelial cells being mtxc pmminent. Large numbers of body defence cells had infiltrated the parenchyma during involution.Immumxyttlchemical staining was performed to identify and investigate the histogenesis of epithelial, myoepthelial and al\8et>lar cells. The cxprcssion o f cytokeratins wa used a s an indicator of histogenetic differentiation of which cytokeratin 18 w m found in both cpithclial and mycxpthelial cells of the goat mammary gland. A decreasc in the number of cytcdceratinexpressing epithelial cells was observed in pregnant alveoli. No staining was o b s e n d in alveolar cells, although cytokeratin 18 w i~s lound in cclls, distinct from thc mycxpithclial phenotype, in alvetdi during lactation.This study demonstrates that the mammary gland of the goat is similar LO the pnmate, rather than rodent, mammary gland. This conclusion is justilicd by the idcntilication of similar ductal structures and TDLUs found in thc pnmate mammary gl...

Milk secretion is modulated by local chemical feedback inhibition, a mechanism that matches supply of milk to the demand. An inhibitor of milk secretion that is present in milk plays a major role in this inhibition. It is a constituent of the whey proteins, and its moleculars mass is in the range of 10,000-30,000 Da.

Changes in milk protein gene expression and specific prolactin binding were quantified in mammary tissue from the tammar wallaby (Macropus eugenii) at different stages of lactation. The transition from early (phase 2) lactation to late (phase 3) lactation was characterized by the induction of the gene for late lactation protein, a novel whey protein. During the same period, the levels of beta-lactoglobulin and beta-casein gene expression increased, whereas there was no change in the levels of expression of alpha-lactalbumin and alpha-casein genes. Prolactin binding in the mammary gland doubled during the latter half of phase 2 of lactation but declined significantly during the transition to phase 3 of lactation. These changes in prolactin binding resulted from changes in the number of receptors and not from a change in the affinity of the receptor for prolactin. Treatment of membranes with concanavalin A increased the number of prolactin-binding sites by 40% in membranes from phase 2 mammary tissue but decreased binding by 40% in membranes from phase 3 tissue, indicating that significant changes had occurred in the membranes of cells during this period. The tammar wallaby can secrete phase 2 and phase 3 milk from adjacent mammary glands (asynchronous concurrent lactation) and the developmental changes in milk protein gene expression and prolactin binding observed during lactation were reflected in these individual glands. Taken collectively, these findings suggest that mammary development and milk secretion in the tammar wallaby are regulated by both endocrine and local (intramammary) mechanisms.

A method of preparing viable cells from dog gastric mucosa is described. Cyclic AMP in these cells is elevated by histamine and 4-methyl histamine but 2-methyl histamine is only a weak agonist. The effects on cyclic AMP levels are inhibited competitively by metiamide and burimamide which give apparent KBvalues of 3.5x10-7 M and 2.3x10-6 M, respectively. These values are similar to those reported for other histamine H2-receptor systems. The H1-receptor antagonists, mepyramine and chlorpheniramine, have no inhibitory effect on the histamine induced elevation of cyclic AMP: promethazine inhibits the system but not by a competitive mechanism. It is concluded that the histamine stimulated adenylate cyclase system is probably located in the parietal cell component.