Über die physiologische Bedeutung der Pterine

This paper comprises a survey of the physiological properties of the pterins, as outlined in the literature. Pterins take part in morphological colour changes, and in this case, they can be considered as light protective pigments. In intermediary metabolism the pterins have been shown to catalyse the oxidation of phenyl-alanine to tyrosine and dopa, while they also seem to prevent the synthesis of melanin in the epidermis of animals. Pterins may play an important part in the sex determination of some insects, for example, stepwise additions of biopterin have some effect on the formation of ovipar females and males in aphids. Pterins are also thought to be involved in the determination of the sex casts of honey bees and ants. Furthermore, some 8-substituted l′.2′-dihydroxyalkyl-pterins containing the L-erythro configuration are known to act as growth factors in mirco-organisms.

Development of contemporary issues courses: pitfalls and opportunities

The development and teaching of contemporary issues courses provide unique opportunities for expanding influence, service to the university, and professional development. During the last decade, there has been a proliferation of such courses centered on the issue of human exploitation of animals. The Ohio State University's general education curriculum, initiated in 1990, includes a requirement that senior students complete a 5-credit course in the category Issues of the contemporary world. Currently, 28 courses are offered in this category, and 5 are from the College of Food, Agricultural, and Environmental Sciences. Our course, entitled Issues concerning the use of animals by humans, was the first from the college included in this category. The course has been offered continuously since 1990-4 quarters per year since 1992. Challenges included gaining approval of the course through a special oversight committee, enhancing visibility of the course outside the college, instructor education, and control of personal biases. The development of this type of course is, necessarily, a continuous process. Instruction of this course has been challenging, enlightening, and exceedingly rewarding. Instructors of similar courses at 11 other universities reported experiences similar to ours.

Effects of heavy metals (Hg2+, cd2+, Pb2+) during the embryonic development of acridid grasshoppers (Insecta, caelifera)

Heavy metals present in the soil get differently accumulated in organisms and show different rates of toxicity at different stages of the life cycle of any organism living there. To see whether such toxicants get accumulated during the embryonic development and/or change the normal developmental processes of organisms exposed to heavy metals, freshly laid eggs and egg pods of two acridids, Aiolopus thalassinus and Eyprepocnemis plorans, were tested against different concentrations of Hg2+, Cd2+, and Pb2+. At increasing Hg2+ concentration in the substrate, an increased egg mortality and reduced nymphal hatching in A. thalassinus were observed, yet no change in the normal duration for embryonic development was noticed. A higher hatching rate of E. plorans nymphs than that of A. thalassinus could possibly be due to the higher tolerance, contributed by larger egg volume and thicker foam around the egg pods of the former. Treated concentrations of Hg2+ could be of sublethal (0.121 &mgr;g Hg2+/g substrate) to lethal (0.605 &mgr;g and more Hg2+/g substrate) doses. The mortality of eggs did not always increase with increasing substrate concentration of Cd2+ and Pb2+, and the hatching rates of both grasshopper species in many cases were even higher than that in the control. Still, lower accumulation factors of Cd2+ and Pb2+ than that of Hg2+ were found coupled with not increased mortality. The tested concentrations of Cd2+ and Pb2+ in the substrates, thus, could be of subacute doses. The embryonic development was found prolonged due to Cd2+ and Pb2+. During parallel egg and egg pod treatments, higher metal concentrations were found in not developed eggs than that in fresh nymphs hatching from the same substrates. This indicated the role of foam around the egg pods as "protective filter" against the toxic substances in the soil.

Autocrine mitogen IgEGF cooperates with c-myc or with the Hcs locus during hepatocarcinogenesis in transgenic mice

Hepatocarcinogenesis is deterministic in transgenic mice expressing in the liver gene construct Alb-DS4 that encodes autocrine growth factor IgEGF (D Stern et al. (1987), Science 235: 321-324), causing their death within 7.1 months. Hepatic expression of construct AAT-myc encoding murine c-myc causes liver cancer in 44% of the mice at 14.8 months. Cooperation of these genes was evident in CD2F1 transgenics bearing Alb-DS4 plus AAT-myc, in which accelerated hepatocellular carcinoma (HCC) formation caused death of all mice within 4.4 months. Alb-DS4 also cooperates with the Hcs locus, which in C3H/HeJ mice mediates high susceptibility to spontaneous hepatocarcinogenesis, causing accelerated formation of HCC to which mice succumbed at 5.1 months. Thus, genes that predispose to HCC formation cooperate in transgenic mice and their interaction is a key to understand mechanisms that cause liver cancer.

Heavy metal content (Hg2+, Cd2+, Pb2+) in various body parts: its impact on cholinesterase activity and binding glycoproteins in the grasshopper Aiolopus thalassinus adults

Various toxicological symptoms were observed in Aiolopus thalassinus (Fabr.) adults which resulted from either contaminated soil or from being fed HgCl2-, CdCl2-, and PbCl2-treated diet. Many insects had abnormal wings which were present until the F3 untreated generation. Heavy metals were stored in different body parts, most of Cd2+ and Hg2+ were found in the testes, followed by the gut. Lead was enriched in all organs and body parts of the treated grasshoppers compared to the control. The highest lead concentrations were found in testes, wings, gut, and ovaries. In the treated generation ChE activity was reduced to about 23% compared to the untreated grasshoppers. In contrast to this, lead increased ChE activity to about 14%. In the following F2 untreated adults, ChE activity was normal; no long-term effect was found. In the supernatant of treated adults a Cd-type glycoprotein was found which can bind Cd ions; its MW was determined by electrophoresis and reference proteins at about 14,450 Da.

Studies of intestinal stem cells using normal, chimeric, and transgenic mice

The mouse intestinal epithelium represents a continuous developmental system. Its four principal differentiated cell types--enterocytes, goblet, enteroendocrine, and Paneth cells--are derived from a common multipotent stem cell located near the base of monoclonal crypts. Members of these four lineages undergo rapid and perpetual renewal along an anatomically well-defined pathway. The gut epithelium provides a unique mammalian model for studying the biological features of stem cells (e.g., their ability to undergo asymmetric division, their enormous proliferative potential, their capacity for functional anchorage in a niche), examining how stem cell hierarchies are established and maintained in renewing cell populations, analyzing the relationships between passage through the cell cycle and lineage allocation (commitment), and defining the mechanisms that give stem cells a "positional address" along the cephalocaudal axis, allowing them to generate regional differences in the differentiation programs of their derived lineages (axial pattern formation).

Expression of SV-40 T antigen in the small intestinal epithelium of transgenic mice results in proliferative changes in the crypt and reentry of villus-associated enterocytes into the cell cycle but has no apparent effect on cellular differentiation programs and does not cause neoplastic transformation

The mouse intestinal epithelium represents a unique mammalian system for examining the relationship between cell division, commitment, and differentiation. Proliferation and differentiation are rapid, perpetual, and spatially well-organized processes that occur along the crypt-to-villus axis and involve clearly defined cell lineages derived from a common multipotent stem cell located near the base of each crypt. Nucleotides -1178 to +28 of the rat intestinal fatty acid binding protein gene were used to establish three pedigrees of transgenic mice that expressed SV-40 large T antigen (TAg) in epithelial cells situated in the uppermost portion of small intestinal crypts and in already committed, differentiating enterocytes as they exited these crypts and migrated up the villus. T antigen production was associated with increases in crypt cell proliferation but had no apparent effect on commitment to differentiate along enterocytic, enteroendocrine, or Paneth cell lineages. Single- and multilabel- immunocytochemical studies plus RNA blot hybridization analyses suggested that the differentiation programs of these lineages were similar in transgenic mice and their normal littermates. This included enterocytes which, based on the pattern of [3H]thymidine and 5-bromo-2'- deoxyuridine labeling and proliferating nuclear antigen expression, had reentered the cell cycle during their migration up the villus. The state of cellular differentiation and/or TAg production appeared to affect the nature of the cell cycle; analysis of the ratio of S-phase to M-phase cells (collected by metaphase arrest with vincristine) and of the intensities of labeling of nuclei by [3H]thymidine indicated that the duration of S phase was longer in differentiating, villus- associated enterocytes than in the less well-differentiated crypt epithelial cell population and that there may be a block at the G2/M boundary. Sustained increases in crypt and villus epithelial cell proliferation over a 9-mo period were not associated with the development of gut neoplasms--suggesting that tumorigenesis in the intestine may require that the initiated cell have many of the properties of the gut stem cell including functional anchorage.

Ethylnitrosourea-induced mutations in vivo involving the Dolichos biflorus agglutinin receptor in mouse intestinal epithelium

A mutagenesis assay system is introduced based on the induction of mutations in somatic cells of mouse small intestine using ethylnitrosourea (ENU). F1 mice heterozygous for the Dolichos biflorus agglutinin (DBA) locus (Dlb-1a/Dlb-1b) encoding the DBA cell surface receptor, were treated in utero on either day 7, day 9 or day 11 post coitum. Mutant intestinal cell populations of adult mice were visualised in whole-mount preparations by the absence of histochemical staining using peroxidase-labelled Dolichos biflorus agglutinin. Loss of staining is attributed to mutagenesis of the Dlb-1b allele in the heterozygote. This system allows one to evaluate mammalian mutagenesis in vivo at a single locus. Mutant cell populations appeared as discrete groups of 'striped' villi, each stripe comprising cells derived from unstained crypt stem cells (cf. Schmidt et al., 1985a). A spontaneous mutation level was noted in untreated controls which was found to differ significantly from that recorded in mice treated with the mutagen (P less than 0.01). The mutation scores were highly consistent among mice and a small number of animals (i.e., 16) were sufficient to detect mutagenic effects of ENU. Thus, the advantages which accrue from the assay are (1) the ability to detect small clones of mutant cell populations in the intestine (i.e., cells derived from a single mutated crypt); (2) a small number of tested mice are required to generate a conclusive result, especially when compared to the mammalian spot test (Fahrig, 1978).

On the clonal origin of tumours--lessons from studies of intestinal epithelium

Clonal studies of adult chimaeric mouse epithelium have demonstrated the monoclonal composition of crypts of Lieberkühn. In neonatal life, however, polyclonal crypts have been found, indicating that crypts are of polyclonal origin. We here relate these findings to studies of mosaic tissues which have addressed the question whether solid tumours are of monoclonal or polyclonal origin. The issues has so far remained unresolved because the expected frequencies of polyclonal tumours, given polyclonal origins, have not previously been estimated. A general approach for the calculation of such expected values is suggested. The consistent reports of tumours with polyclonal components suggest that autocrine or paracrine mechanisms play an important role during tumorigenesis.

Economics of using bovine somatotropin in dairy cows and potential impact on the US dairy industry

Budgets with a microcomputer spreadsheet were developed to evaluate the economics of bovine somatotropin use and to estimate the impact on US dairy cow numbers. Income over feed and variable costs increased with somatotropin use and low feed prices. With high feed prices, income responses were less favorable, and when combined with low milk prices, somatotropin use resulted in less income than from control cows. Price of somatotropin did not have a major effect on production costs. The number of cows needed to meet US milk requirements is primarily influenced by per capita consumption and production per cow. With continuing yearly increases in per capita consumption of 2 kg of milk equivalent and cow milk yields of 114 kg, the number of milk cows needed through 1992 remains at the 1987 figure of approximately 10.3 million. In the scenario of a 15% increase in milk yield due to somatotropin, 20% of cows receiving the hormone, and cows receiving the hormone being 10% above the national average of all cows; the number needed in 1992 is 9.77 million, or a drop of 5.4% from 1987. Somatotropin use will have a less drastic effect on cow numbers than originally predicted.

Development of the pattern of cell renewal in the crypt-villus unit of chimaeric mouse small intestine

We have previously shown that the epithelium of each adult intestinal crypt in chimaeric mice is derived from a single progenitor cell. Whether the crypts are monoclonal from the outset-that is, are formed by the proliferation of a single cell-or whether their formation is initiated by several cells was not known. Here we report that many crypts contain cells of both chimaeric genotypes in the neonatal period indicating a polyclonal origin at this stage of morphogenesis. The cellular organization of the early neonatal crypt is therefore different from that of the adult crypt, which includes a zone of 'anchored' stem cells above the crypt base. Within 2 weeks, however, the crypt progenitor cell and its descendants displace all other cells from the crypt and the crypt attains monoclonality. The distribution of enterocytes on chimaeric villi in the neonate shows a mottled pattern of mosaicism which is progressively replaced by coherent sheets of cells from the crypts, and within two weeks the orderly adult clonal pattern is established.

Immunochemical demonstration of the clonal organization of chimaeric mouse epidermis

The clonal organization of chimaeric mouse epidermis was demonstrated by in situ staining of whole-mount preparations using monoclonal antibodies directed against H-2k and H-2b antigens. A striking pattern of transversely oriented stripes or patches was found which extended from mid-dorsum to the flank region. The orientation of these patches indicates a preferred directional expansion of clones during the development of dorsal/lateral epidermis. The clonal pattern of the belly region differed in that stripes were not found, but a marked ventral midline boundary was observed. This demarcation line may be due to a physical effect, i.e. isolation of the left and right ventral halves of the epidermis during early embryogenesis with relatively little cell mingling following closure of the abdominal wall. The obvious nonhomogenous distribution of chimaeric components in dorsal/lateral and ventral epidermis contradicts assumptions of homogenous, fine-grained patchiness derived from electrophoretic analysis of tissue samples and used in studies of skin carcinogenesis. The observation that hair follicles may contain cells of both parental genotypes implies a polyclonal origin. Epidermal proliferative units as described by Potten (1974) were not revealed by the pattern of mosaicism at the cellular level in these chimaeric tissue sheets. This indicates that the proliferative compartment of each putative epidermal unit is polyclonal.

Calculating numbers of tissue progenitor cells using chimaeric animals

Experimental chimaeras have been used to estimate the number of tissue progenitors from the variation in the proportions of cells of each genotype that can be found in a given tissue. However, because of a failure to appreciate the importance of assessing the extent of agreement required between the predictions made by a specific mathematical model and the actual data, we believe that the statistical procedures were inappropriate and have led to unjustified conclusions. We illustrate our argument by reference to published data on the number of progenitor cells in the facial nerve nucleus of the mouse (K. Herrup, T. Diglio, A. Letsou, (1984). Dev. Biol. 103, 329-336).

Immunohistochemistry in the analysis of mouse aggregation chimaeras

We have used cellular mosaicism in chimaeric mice to study the clonal organization of normal tissues. The mosaicism has been demonstrated in sections and in whole mounts of intestinal epithelium, aortic endothelium and retinal pigment epithelium using H2 antigens and a carbohydrate polymorphism recognized by Dolichos biflorus lectin as strain-specific markers. The results show that the epithelium of each adult intestinal crypt is derived from a single progenitor cell. Because crypts of differing genotype may contribute cells to the same villus, the pathways of cell migration up the villi can be demonstrated. The ability to stain mosaic patches in two dimensions in large intact sheets of epithelium has permitted a more satisfactory analysis in terms of clonal development than was previously possible with data from tissue sections. We have adapted statistical procedures from plant ecology to examine the scale of clustering of patches of like genotype, and thence to recognize 'descendent' clones, i.e. groups of cells which are not contiguous, but are related by descent from a common ancestor in embryogenesis.

Clonal analysis of chimaeric patterns in aortic endothelium

The mosaicism in aortic endothelium of mouse aggregation chimaeras is demonstrated using the lectin Dolichos biflorus agglutinin as a strain-specific marker. The general fragmentary appearance and considerable size range of patches suggests that endothelial cells do not proliferate in a highly coherent manner. The developmental significance of the observed patterns is investigated by means of a quantitative statistical analysis-the Greig-Smith analysis of variance. This method examines the spatial distribution of patches and is able to detect and characterize pattern at various scales. The results show that (1) patches are non-randomly distributed at all scales examined and (2) 'clusters of clusters' occur at one small and one large scale, defining territories of 'primary' and 'secondary' descendent clones, which arose respectively during early and late periods in the development of the endothelium. We conclude from this analysis that (1) cell mixing is never complete, even in the early embryo and (2) cell mingling is not uniform during development. A different pattern was previously demonstrated for intestinal epithelium (Schmidt, Wilkinson & Ponder, 1985c) indicating the potential value of the method for quantitative comparison of mosaicism between tissues and also different developmental stages. Our results suggest that the analysis of patch sizes is likely to be less informative in terms of developmental mechanisms, than the analysis of the spatial arrangement of patches.

Non-random spatial arrangement of clone sizes in chimaeric retinal pigment epithelium

Clonal analysis of whole-mount preparations of entire retinal pigment epithelium (RPE), using SWR in equilibrium C57BL/6JLac and DDK in equilibrium C3H/Bi mouse aggregation chimaeras in which one of the two parental components predominated, revealed a markedly non-random spatial arrangement of patch (clone) sizes. Single-cell and small patches predominated in an area around the optic nerve head while large patches occurred most frequently near the periphery. Mechanisms are discussed which may explain these results. Patch size frequency distributions were concave and skewed. Singletons were the most frequent size class, but a wide range of sizes and a smaller number of much larger patches were also always found. The results preclude the use of statistical methods previously employed to calculate clone sizes from the geometric means of observed patch sizes. Instead, the median and interquartile range may provide the best summary of the observed patch size frequency distributions. Our findings support a stochastic model of tissue growth.

Detection and characterization of spatial pattern in chimaeric tissue

The mosaic pattern of patches of crypts of Lieberkühn in chimaeric C57BL/6JLac (B6)----DDK mouse small intestine, demonstrated using Dolichos biflorus agglutinin as strain-specific marker, is quantitatively examined using the Greig-Smith analysis of variance. This analysis, widely used in ecological research, provides a method to detect and characterize pattern at various scales. The analysis demonstrates that B6 patches are non-randomly distributed at all scales examined. A consistent increase in the intensity of pattern at one particular scale over all replicate samples identifies 'clusters of clusters' which probably are territories of 'descendent' clones. The sizes of descendent clones, either in terms of numbers of patches or total numbers of crypts, are highly variable. A steady reduction in the strength of pattern from proximal to distal is found. The Greig-Smith analysis of variance provides a valuable method for the analysis of pattern in chimaeric tissue.

Derivation of mouse intestinal crypts from single progenitor cells

Adult intestinal epithelium consists of a sheet of single-cell thickness which is morphologically highly organized into tubular invaginations (crypts) and finger-like projections (villi). Proliferation of the cells is confined to the base of the crypts, from which cells migrate to the villi, where they are shed. The villi are formed during embryogenesis from a multilayered epithelium. In mice, crypts develop at about the time of birth from the epithelium between the villi, which by this stage is no longer multilayered. So far it has remained unknown how many progenitor cells contribute to each crypt, and whether they develop by the proliferation of already committed progenitors, or as a result of local inductive tissue interactions. Here, we have used mouse aggregation chimaeras as an experimental system to demonstrate immunohistochemically that the epithelium of individual crypts in small and large intestine of adult mice is always composed of cells of a single parental type. We have confirmed that this result is not an artefact of the chimaeric system by examining female mice that are mosaic for the X-linked alleles Pgk-1a and Pgk-1b. We conclude that the epithelium of each adult crypt is derived from a single progenitor cell.

Cell migration pathway in the intestinal epithelium: an in situ marker system using mouse aggregation chimeras

The cell migration pathway in the intestinal epithelium of DDK in equilibrium C57BL/6JLac mouse chimeras is demonstrated using Dolichos biflorus agglutinin-peroxidase as strain-specific marker. Cell sheets of one genotype extend in relatively straight lines from crypt to villus apex. Narrow sheets are mostly interrupted in the distal two-thirds of duodenal but not ileal villi, suggesting that in the duodenum cell loss occurs below the apical extrusion zone. These differences between duodenum and ileum correspond to differences in villus shape. The pattern of cell migration in Peyer's patch epithelium is consistent with that of the duodenum. In chimeric colon, sharply demarcated territories of crypts with a narrow cuff of surface epithelium represent the counterpart of the villus/crypt unit of the small intestine.

Clonal analysis of intestinal crypt populations in mouse aggregation chimaeras

The epithelium of each individual intestinal crypt in adult mouse aggregation chimaeras is composed of cells of a single parental genotype (Ponder et al. 1985). Using a carbohydrate polymorphism recognized by Dolichos biflorus agglutinin as a strain-specific marker on entire sheets of intestinal mucosa, we have analysed the two-dimensional mosaic patterns of patches of the chimaeric intestinal crypt population. The relative proportions of each genotype varied greatly along the length of any one intestine. In chimaeras with highly unbalanced proportions, the minority component occurred as discrete patches. Patches of single or a few crypts were most frequent, but a smaller number of much larger patches was always present. The size frequency distribution of discrete patches was highly concave and departed significantly from a geometric distribution (a model for non-differential proliferation), but fitted the more skewed negative binomial model. The data are consistent with the interpretation that most progenitor crypts never or rarely divide, while a minority proliferate to a greater extent. We discuss ways in which our system could be analysed further to examine this interpretation. Our results also support Whitten's (1978) conclusion from a computer simulation that the mean patch size, as it has previously been used in statistical analyses of chimaeric tissue, 'is not a reliable statistic on which to judge mosaicism'.

A method for the preparation of large intact sheets of intestinal mucosa: application to the study of mouse aggregation chimeras

A technique for the preparation of entire intestinal mucosal sheets is described that renders the population of crypts accessible for two-dimensional study. We have applied the technique to demonstrate the mosaic crypt populations in the intestinal epithelium of mouse aggregation chimeras, using the lectin Dolichos biflorus agglutinin (DBA) as a strain-specific histochemical marker.

Effectiveness of educational efforts in implementing mastitis control procedures in commercial dairy herds

One hundred-fifty diarymen in north-eastern Ohio, whose herds had a history of persistently high Wisconsin Mastitis Test scores, were invited to participate in this project, with 43 agreeing to do so. These dairymen were divided into two experimental groups and one control group to determine the effectiveness of two intensities of educational effort on adoption of mastitis control procedures and to demonstrate the effectiveness of mastitis control recommendations. A teat dipping and dry cow therapy program was adopted by more herds in the group with intense educational effort than in the intermediate or control group. Percents of herds in each group utilizing this program in 1977 (start of project), 1978, and 1979 were 8, 75, and 92 for the intense group; 30, 50, and 50 for the intermediate group; and 10, 27, and 27 for the control group. Prevalence of infection declined more rapidly in the intense group with 42, 28, and 24% of cows infected; 39, 25, and 30% in the intermedia, and 56, 35, and 42% in the control group in 1977, 1978, and 1979. Those herds adopting a teat dipping and dry cow therapy program had infection prevalence of 41, 25, and 20% of cows; bulk tank Wisconsin Mastitis Test scores of 15.5, 14.7, and 11.4; and milk production per cow per day of 18.4, 18.4, and 17.5 kg in 1977, 1978, and 1979.

Mammary implant shell failure

The author critically examined removed implants, and found that the sac of both inflatable and gel mammary implants may perforate due to wear or erosion.

Experience with the Ribeiro reduction mammaplasty technique

The advantages and disadvantages of the Ribeiro reduction mammaplasty are cited. It is a very good technique when used with the described modifications in properly selected patients.

Change in udder health and overmilking

Removing milker units as soon as milk flow stopped was compared to milking for a fixed time of 12 min in an 8-wk trial with 60 cows. Teats were dipped in broth culture of approximately 10(9) colony forming units per ml of Staphylococcus aureus, Streptococcus agalactiae, and Streptococcus uberis for 4 wk. More new infections of quarters occurred in the 12-min group. In trials 2 and 3, 20 additional cows were milked with automatic milking machine detachers and 20 cows were milked with a flow control unit for 12 min each trial. New infection rates were highest in the two groups milked for 12 min. Age for lactation and cows were associated with most of the variation in the new infection rate. Cows with pointed teat ends had the highest rate of new infection. Effects of fixed-time milking on increased mammary infection and clinical mastitis were small.

Release of oxytocin in the cow during milking

Jugular vein oxytocin concentrations were determined at 15-s intervals on 10 Holstein cows during milking. Oxytocin ranged from .5 muU/ml plasma prior to udder washing to 652.7 muU/ml plasma at 1 min after application of teat cups. The results indicate a gradually increasing release of oxyctocin after stimulation and a maximal oxytocin release 1.5 min after start of udder washing and 1 min after teat cup application.

Epinephrine inhibiting milk ejection in lactating cows

Blood oxytocin was determined on 10 Holstein cows during normal milking and during milking when epinephrine was injected intravenously before or after udder stimulation. The average peak oxytocin concentration during normal milking was 399.7 muU/ml plasma and was reached at 1 min after teat cup application. Oxytocin concentration in blood plasma declined rapidly after peak concentration and dropped to 30.5 muU/ml plasma within 4 min after the start of milking. By 5 min after removal of the teat cups, it had declined to less than 4 muU/ml plasma. The administration of epinephrine, either before or after udder washing, inhibited milk ejection as indicated by milk production and oxytocin concentrations. Peak oxytocin concentrations were 1.05 muU/ml plasma 1 min after teat cup application when epinephrine was injected before udder washing and 8.6 muU/ml plasma at teat cup application when epinephrine was injected after udder washing. These results and the use of a beta receptor blocker to inhibit the effect of epinephrine at the myoepithelial cell level indicated that epinephrine inhibited release of oxytocin from the neurohypophysis.