J. Anat. (1979), 129, 1, pp. 117-140 With 12 figures Printed in Great Britain
The ultrastructure of the sweat glands of the ox, sheep and goat during sweating and recovery D. McEWAN JENKINSON, I. MONTGOMERY AND H. Y. ELDER
Departments of Physiology, The Hannah Research Institute, Ayr and the University of Glasgow
(Accepted 4 July 1978) INTRODUCTION
The patterns of cutaneous evaporative loss obtained from mammals in warm environments using ventilated capsules are largely due to sweating. They vary markedly between species (Allen & Bligh, 1969). Cattle exhibit a stepwise increase in cutaneous moisture loss to a level which is maintained (McLean, 1963 a). The sheep and goat on the other hand show discrete intermittent discharges of sweat which gradually decline in size to what has been termed 'fatigue' (Bligh, 1967; Robertshaw, 1968). The pattern in the cow has been attributed to the effect of myoepithelial contractions superimposed upon a rapidly rising secretory rate, and that of the sheep and goat to myoepithelial expulsion of sweat, the secretory process being slow and uncontrolled (Bligh, 1967). There is, however, very little information on the secretory mechanisms in these three species. The concept of an active secretory process in cattle is supported by evidence from studies of the ionic composition of bovine sweat (Johnson, 1970; Jenkinson & Mabon, 1973). Heat and exercise cause a reduction in glandular volume (Hayman & Nay, 1958; Findlay & Jenkinson, 1964), indicating myoepithelial expulsion of sweat. However, the light microscope fails to reveal either necrobiotic discharge from, or changes in, the secretory epithelium, or alterations in the myoepithelium, during sweating (Findlay & Jenkinson, 1964). Thus, information on the ultrastructural appearance of the sweat gland is required before the modes of secretion and expulsion of sweat in cattle can be elucidated. Although the cytology of the resting gland has been described (Prasad, 1973) the effects of stimulation on its ultrastructure are unknown. In the sheep and goat the 'fatigue' of the glands is apparently due to the rate of expulsion exceeding that of sweat production (Jenkinson & Robertshaw, 1971; Johnson, 1973). In the goat, light microscopy discloses, as in cattle, a decrease in volume of the gland during sweating, and supports the view of sweat expulsion by myoepithelial action; this change is accompanied by a thickening of the glandular wall (Jenkinson & Robertshaw, 1971). The ultrastructure of the gland, even at rest, has not been described. The methods of sweat production and expulsion in cattle, sheep and goats are, therefore, still incompletely understood. More information about the similarities and differences in the modes of secretion in these species should aid understanding of the basic mechanism of secretion in mammals in general. The present work was, therefore, undertaken to provide evidence on the mode of sweat secretion in the cow, sheep and goat by studying the ultrastructural appearances of the sweat 0021-8782/79/2828-000 $00.00 ©1979 Anat. Soc. G.B. & I.
D. McEWAN JENKINSON AND OTHERS
Table 1. Skin sampling times during the sweat gland recovery period, measuredfrom the time of leaving the hot environment Environmental Animal Sheep 3
Sheep 5 Goat 1 Goat 2 Goat 3 Goat 5
temperature max/min (°C) 12
Sampling times (h-min) , 1
0-25 1-0 1-0 0-15 0-10
3-0 3-0 2-0 0-30 0-40
6-0 3-0 1-0 1-45
10-0 5-0 4-0 2-30
24-0 10-0 5-0 4-0
24-0 10-0 9-0
11/9 21/19 13/9 13/9 12/10
glands before and at intervals after induction of sweating in controlled warm environments. A preliminary account has been published (Elder, Jenkinson & Montgomery, 1977). MATERIALS AND METHODS
Four 11 months old Ayrshire oxen, 5 adult castrated male Dorset Horn x Finnish Landrace sheep, and 5 adult British Saanen goats (3 females and 2 castrated males) were subjected to controlled conditions of temperature and humidity in a climatic chamber (Findlay, McLean & Bennett, 1959). All were fed a standard complete diet with water ad libitum and between experiments were housed in thermoneutral or cool environments.
Measurement of sweating activity Cutaneous moisture loss was continuously recorded, using the ventilated capsule technique of McLean (1963 b), from an area of shaved skin overlying the eighth and ninth ribs midway between the thoracic spinous process and the sternum. Since the mode of secretion characteristic of each of the three species occurs synchronously on both sides of the thorax (Findlay & Robertshaw, 1965; Allen & Bligh, 1969), skin samples were removed by biopsy, using the high speed punch technique of Findlay & Jenkinson (1960), at various time intervals from the equivalent site on the opposite side of each animal.
Cattle The four oxen were placed in an environment of 20 °C DB (dry bulb)/16 °C WB (wet bulb) for a period of 6-7 hours and cutaneous evaporative loss was monitored throughout. A skin specimen was obtained from each animal immediately upon entry into the controlled climate, and at the end of the experimental period before removal from the climatic room. The following day the experiment was repeated in an environment of 40 'C DB/26 °C WB with the difference that skin samples were taken at the times given in Figure 1. Sheep and goats Five sheep and 2 goats were subjected to 15 °C DB/10 °C WB for a period of 3 hours and cutaneous evaporative loss was again measured continuously. Skin
Sweat gland ultrastructure 40 °C DB/260C WB 72 C
0 o 0L
~~~~~~~~~142-29gm-2 h -I
4 Time (hours)
Fig. 1. The patterns of cutaneous evaporative loss from four oxen in an environment of 40 °C DB/26 °C WB. Skin samples were taken from the contralateral side of the animal at the times shown (numbered arrows).
samples were taken immediately upon entry into, and again before removing the animals from, the chamber. The following day the animals were induced to sweat by placing them in an environment of 40 °C DB/26 °C WB or 30 °C DB/28 °C WB, and skin samples were taken from the contralateral side before and during sweating as shown in Figure 2. Three additional goats were subjected to 40 "C DB/26 "C WB and sampled before and at the end of the exposure after sweat gland 'fatigue'. These, with one of the other goats and three of the sheep, were sampled at the times shown in Table 1. To provide a range from 'fatigue' during the recovery period, the samples were taken at intervals in the cool environment measured from the moment the animals left the hot environment.
Histology The skin specimens were fixed for 3 hours in 2 % glutaraldehyde in 0 1 M sodium cacodylate buffer at pH 7-3 (Sabatini, Bensch & Barmett, 1963) and washed in 0-1 M sodium cacodylate buffer (pH 7 3) for a minimum of 4 hours. Post-fixation was carried out for 1 hour in 1 % osmium tetroxide in the cacodylate buffer. The tissues were then dehydrated through graded acetone solutions, cleared in propylene oxide and embedded in Epon-Araldite. Ultrathin sections were cut from each block, stained in alcoholic uranyl acetate followed by lead citrate (Reynolds, 1963) and examined in an AEI EM6B electron microscope at an accelerating voltage of 60 kV.
D. McEWAN JENKINSON AND
2 -1 0
2 3 Time (hours) Fig. 2. The patterns of cutaneous evaporation from 5 sheep and 2 goats in an environment of 40 °C DB/26 °C WB. Skin samples were taken from the contralateral side at the times indicated. 1
Patterns of evaporative loss The patterns of cutaneous evaporative loss, each to its own base line, found in the four oxen when subjected to a warm environment, are shown in Figure 1. Although there was some variation in the magnitude of the response obtained, the patterns were essentially similar in all four oxen. Sweating was not observed during the control period in the cooler environment.
The unstimulated gland The ultrastructure of the gland in samples taken prior to sweating at 40 °C was indistinguishable from that obtained in specimens taken before and during exposure to the control temperature of 20 'C. The combined results are summarised in the diagram (1 a). The flattened secretory epithelium was surrounded by a myoepithelium and a well-developed basement membrane (Fig. 3a) and the entire fundus was enveloped in a fenestrated fibrocyte sheath. The myoepithelial cells were attached by hemi-desmosomes to the basement membrane and by desmosomes to adjacent cells and secretory cells (Fig. 3 a, b). The secretory cells were linked by basal dovetailing (Fig. 3b) and an apical junctional complex complete with desmosome and zona occludens (Fig. 3b). The glandular lumen contained a fibrous-like macromolecular colloid.
Sweat gland ultrastructure