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Testicular vasomotion in different mammals

Ola Collin, Jim L. Zupp1,  Brian P. Setchell1

Department of Integrative Medical Biology, Section for Anatomy, Umeä University, Sweden 
1Department of Animal Science, University of Adelaide, Australia

Asian J Androl  2000 Dec; 2:  297-300

Keywords: testis; vasomotion; human; rats; possum; rams; mice; tammar-wallaby
Abstract
Vasomotion is a rhythmical variation in arterial blood flow present in many different organs among them the rat testis. Vasomotion is suggested to play an important role for the transvascular fluid exchange and the exchange of nutrients over the capillary wall as well as the formation of interstitial fluid. The present study was undertaken to elucidate whether vasomotion is present in the testes of different species independent of their anatomical vascular topography. Blood flow in the testes of mouse, brush-tailed possum, tammar wallaby, ram and human was investigated by using a laser Doppler flowmeter. Vasomotion was found in all the species investigated.
1 Introduction
Rhythmical contraction and dilatation of small arteries and arterioles causing changes in blood flow are observed in a variety of tissues and species. This phenomenon is referred to as vasomotion and is separated from other regular cycles such as heartbeat, breathing and for the testis contractions of the capsule. The role of vasomotion has been widely discussed and it is suggested that it is essential for the exchange of nutrients, is involved in the formation and resorption of interstitial fluid and facilitates the flow of lymph from the capillaries to the lymph vessels. During periods of slow blood flow net filtration from the interstitial tissue to the vasculature occurs and during high flow filtration from the vasculature take place[1,2]. Inhibition of vasomotion in the rat testis restricts fluid resorption to the vasculature[3,4]. When studying the microcirculation in rat testes by using laser Doppler flowmetry a consistent vasomotion pattern was found of 7-11 peaks/minute[5,6]. The factors controlling vasomotion are not fully understood. The classical theory of vasomotion involves a pacemaker cell in the endothelial wall[1], which spontaneously depolarises and produces rhythmic discharge of action potentials. The activity of such a cell would be propagated through the tissue and cause a wave of contraction along the artery. In the testis vasomotion is influenced by hormones and other factors, e.g. it is induced by sexual maturation, hCG[7] and testosterone[8] and inhibited by hypoxia, cryptorchidism, varicocele and by locally produced vasoconstrictors such as 5-HT and ET-1[9,10]. We have also shown that external factors, such as temperature[11] and cigarette smoke[12] affect vasomotion. In all organs the control of blood flow is important but for the testis it may be particularly critical as the oxygen concentration in the seminiferous tubules is very low, almost on the brink of hypoxia[13-16]. To investigate further the value of our earlier studies when it comes to application to other species e.g. human, we wanted to discover whether vasomotion is present in testes in other mammals in spite of the wide variation in anatomical topography. We therefore investigated blood flow in the testes of some other mammals, using the laser Doppler technique.
2 Materials and methods

2.1 Animals

The animals used were adult mice (4, 5WARI strain, bred in the Department of Animal Science), brush-tailed possums (Trichosurus vulpecula, 2, trapped in the Adelaide suburbs), tammar wallabies (Macropus eugenii, 2, from the colony at Flinders University) and Merino rams (5, from the flock of the Department of Animal Science). The mice and the possums were kept in a light and temperature controlled animal house, the wallabies in yards at Flinders University and the rams in paddocks adjacent to the Department of Animal Science. Food and water was available ad lib, but the rams were kept off food for 48 h and off water for 24 h before anaesthesia. On the day of experiment, the animals were anaesthetised: mice; pentobarbitone sodium, 6 mg/mL, 1 mL/100 g body weight, possums; avertin 15 mL I/P of a solution made from 1 g tribromoethanol and 0.5 g amylene hydrate in 1  mL water, diluted with 4 mL ethanol and then made to 50  mL with saline and Rompun (Bayer) 20 mg in 1  mL I/M, wallabies; Isoflurane (Abbott) by mask, rams; pentobarbitone sodium 60 mg/mL, 0.25  mL/kg body weight I/V, with supplementary doses of 0.05 mL/kg as needed.

The blood flow in the human testis was observed prior undergoing surgery, orchidectomy, as treatment of prostatic cancer.

2.2 Blood flow

Blood flow was recorded using a laser Doppler flowmeter (PF 4001 Master, Perimed AB, Stockholm, Sweden) as previously described[4-5]. Laser light was emitted through a probe and the back scattered light converted to an electrical signal, which was transferred on line to a PC (Compaq LTE Lite 4/25). The recorded signal was subsequently analysed for blood flow, frequency and amplitude using the Perisoft software v.5.10 (Perimed AB) to give values for frequency (as peaks per minute), blood flow and amplitude (in perfusion units). These perfusion units are arbitrary units which should not be translated into absolute transfusion units. However, results from the same instrument can be compared as well as results between instruments if the same method for calibration has been used.

2.3 Experimental procedure

The scrotum of each animal was washed, shaved and sterilised, and a small incision made in the scrotal skin and tunica vaginalis on the ventral side of the left testis of the smaller animals. A laser probe (multireceiver PF412, Perimed, Stockholm, Sweden) was placed 0.5 mm over the testicular surface. In the ram and human, the incision was made in the anterior surface of the scrotum, and because blood flow could not be recorded because of the thickness of the tunica albuginea, a needle probe (PF 403) was inserted through a thin plastic guide tube into the testis parenchyma. The probe was left undisturbed for five minutes and then  blood flow was recorded for a further ten minutes.

3 Results

All animals investigated showed vasomotion with a regular frequency and amplitude. Those parameters showed no consistent difference depending on species  (Figure 1). In the mouse the frequency was between 5 and 8 peaks/min the flow average 115 perfusion units PU and an amplitude of 80 PU. In the possum the frequency was 5-6 peaks/min, the flow average 135 PU and an amplitude of 100 PU. In the wallabies, the frequency was 8-12 peaks/min, the flow was average 480 PU and an amplitude of 80 PU. In the ram the frequency was 9-15 peaks per minute, average flow 140 PU and an amplitude of 80 PU and in man the frequency was 7-8 peaks per minute, average flow was 150 PU and the amplitude 130 PU. As erlier found the rat has a frequency between 7-11 peaks/min an amplitude around 100 PU and an blood flow level with a mean at 150 PU.

Figure 1. Showing one curve from each species (A-ram, B-mouse, C-possum, D-human, E-rat, F-tammar wallaby). On Y axis perfusion units and on X-axis time.

4 Discussion

Vasomotion can be demonstrated in the testes of a range of mammals, and there are no consistent differences (except from the high blood flow level in Wallabies, could be due to stress[17]) between species with regard to blood flow level, frequency or amplitude. These findings increase the likelihood that these periodic variations in blood flow could be important in the normal functioning of the tissue.  It is important to realise that the capillaries in the rat testis show cyclic variation in diameter, which are synchronised between capillaries supplied from the same arteriole[3], and these changes in diameter are thought to be responsible for the changes in blood flow recorded with the laser-Doppler probe. The exact role of vasomotion in testis function, or indeed in the function of any tissue in which it has been found is still a matter for discussion[1,18]. However, it seems likely that vasomotion may be important in regulating fluid transfer between the vasculature and the tissue[2]. It is interesting that it is not seen in prepubertal rats or in adults after treatment with hCG[5] and disappears if the Leydig cells are destroyed with ethane dimethane sulphonate (EDS), but returns if the animals are treated with testosterone[19,8]. Vasomotion is also sensitive to variations in testis temperature, disappearing if the testis is heated to between 36 and 42, and becoming much slower in frequency, but with a large increase in amplitude of the temperature falls below normal[11].

We have no explanation for the difference between the present results with mice, and those of a previous study[20], in which vasomotion was not apparent in the testes of mice, using a technique which revealed it clearly in rats. The same anaesthetic was used in both studies, although the mice were of a different strain. Depth of anaesthesia may be important, since vasomotion is inhibited in many tissues in anaesthetised animals[21], but it is not possible to compare the two studies in this regard. The mice in the earlier study was probably physically stressed (A. Bergh, personal communication), and it is now known that stress inhibits vasomotion in the rat testis[17]. From the present results, it is now clear that vasomotion in the testis is the rule, rather than that the rat is unusual. Maybe one can use the observation of vasomotion in the human testis as a rough mesaurememnt of the state of the testis. Further on it will be interesting to examine species like the pig, horse or bandicoots, in which a large proportion of the interstitial tissue is occupied by Leydig cells[22] or species with inguinal or abdominal testes.

Acknowledgements

This work was supported by grants from the Swedish Medical Research Council (project 5935), the Maud and Birger Gustavsson foundation and the JC Kempe Memorial Foundation. We like to thank Dr. R.V. Baudinette, Flinders University for supplying us with the wallabies and assisting with their anaesthesia.

References

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Correspondence to: Dr. Ola Collin, MD, PhD, Department Integrative Medical Biology,  Section for Anatomy, Umeå University, S-901 87 Umeå, SWEDEN.
Tel: +46-90-786 5140   Fax: +46-90-786 5480  
e-mail: Ola.Collin@anatomy.umu.se
 Received 2000-10-08     Accepted 2000-11-19