1 Department of Obstetrics and Gynaecology, University of Göteborg, Sahlgrenska University Hospital, SE 413 45 Göteborg, 2 Department of Histology, University of Göteborg, SE 413 90 Göteborg and 3 Department of Women's and Children's Health, Section of Obstetrics and Gynaecology, University of Uppsala, Akademiska Sjukhuset, SE-751 85 Uppsala, Sweden
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Abstract |
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Key words: blood vessels/ectopic pregnancy/oviduct/prostaglandin/vasopressin
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Introduction |
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The tuboovarian blood flow may also have pathophysiological significance, e.g. in the case of ectopic implantation. More than 95% of such gestations are located in one of the oviducts, and the adnexal circulation is crucial to maintaining such pregnancies.
In a large proportion of tubal implantations, the growth of the trophoblast sooner or later gives rise to rupture of these vessels, which may result in serious intra-abdominal haemorrhage. With the introduction of the new therapeutic procedures for tubal pregnancies, including conservative laparoscopic surgery (Pouly et al., 1986) and local injection therapy (Lindblom et al., 1987
; Lang et al., 1990
), interest has been directed to the effects of vasoactive agents on these vessels.
In laparoscopic surgery, haemostasis represents an everyday problem and diffuse bleeding may occur in a variety of other interventions, e.g. myomectomy, adhesiolysis or resection of ovarian cysts. Locally acting haemostatic agents may serve an important purpose in this regard, but the information about the effects of different agents on this vasculature is still fragmentary.
The aim of the present study was to compare the response of resistance arteries of the human mesosalpinx to certain vasoconstrictive agents, i.e. the vasopressin analogues lysinevasopressin and triglycyl-lysinevasopressin as well as the adrenoceptor agonist adrenalin and prostaglandin F2.
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Materials and methods |
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Two arterial segments, both 3.0 mm long according to a microscope scale, were isolated by use of microscissors and mounted in specially designed gallows used for recording transversal wall tension in small blood vessels (Norén et al., 1990). These gallows, which were used instead of the more commonly used metal hooks (e.g. Karlsson et al., 1997
), were immersed in a mantled 50 ml tissue chamber filled with HEPES buffer. The temperature was kept at 37°C and the solution was continuously gassed with 100% oxygen, giving a pH of 7.37.4. The gallows were connected to a force transducer (Grass FTO3; Grass Instruments, Quincy, MA, USA), and contractile activity was recorded isometrically under a passive tension of 5 mN (Figure 1
). Before being exposed to drugs, the specimens were allowed to equilibrate under the applied passive tension for 60 min. The gallows equipment is similar in function to the more commonly used hook system (cf. Karlsson et al., 1997
).
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The concentration of a certain compound that causes 50 and 100% of the maximum effect is designated EC50 and EC100 respectively. To determine potency, cumulative concentrationeffect curves were constructed and EC50 values were calculated, assuming that the responses followed the law of mass action. For each compound, the maximal response (efficacy) was determined.
Statistics
In the contractility experiments, an overall analysis of variance with repeated measures was performed. For comparison of changes when a new compound was added, Wilcoxon's sign rank test for matched pairs was used. A P-value of 0.05 was considered significant.
To confirm that the vessels were, in fact, arterial segments of a size corresponding to resistance arteries, a special series of histological experiments was conducted. Segments of blood vessels were collected randomly from 10 patients and fixed in 4% buffered formaldehyde (pH 7.4) for 4 h and rinsed in 10% sucrose in phosphate-buffered saline (PBS)buffer solution (pH 7.4). After dehydration with increasing concentrations of ethanol and xylene, the specimens were embedded in paraffin. Sections (3 µm thick) were photographed with a Nikon Optiphot microscope using Kodak Tri-X Pan film. A metric microscale was photographed and used to measure the diameter and thickness of the vessels.
The study was approved by the Ethics Committee of the University of Göteborg.
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Results |
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In experiments adding a third compound to two others, the response was enhanced in all groups. The augmentation for adrenalin as a third compound was 1.7 ± 0.9 mN (P < 0.001), for LVP as a third compound 0.9 ± 0.4 mN (P < 0.01) and for PGF2 0.2 ± 0.1 mN (P > 0.10, ns).
The results of the analysis of variance showed that the `repeat' factor was significant (P < 0.001). Treatment was also significant (P = 0.015), i.e. it mattered in what order the drugs were given. The three treatments were regarded as the three orders in which the drugs were given.
The velocity of contraction induced by LVP, adrenalin and PGF2 was studied by registration of muscle activity with extended time scale. Adrenalin constantly had the highest contraction velocity (0.4 ± 0.023 mN/s). LVP and PGF2
exhibited significantly slower contraction velocity. The PGF2
response was of a biphasic character in 56% of instances (Figure 5
).
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Discussion |
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All the compounds tested were powerful vasoconstrictors. It should be emphasized that in individual cases the effect of the first compound was weak, and a considerably more powerful contraction was produced by the second compound (cf. Figure 4). Among the compounds studied, lysine vasopressin was the most potent on a molar basis. The potency of PGF2
was similar to that of adrenalin. Adrenalin and lysine vasopressin produced similar maximal response, i.e. had similar efficacy, whereas PGF2
induced the weakest response of the four agents.
The comparisons of `time to maximal response' showed that adrenalin had the highest contraction velocity. The observed difference in contraction velocity may indicate different modes of action. This is compatible with the finding that the compounds could reciprocally augment one another's maximal response. The differences in contraction velocity may reflect utilization of different calcium pools intracellularly and/or at the membrane receptor level. Theoretically, a compound with a fast onset (adrenalin) acts preferentially by increasing the calcium influx through receptor-operated channels (Andersson and Högestätt, 1984). Likewise, compounds with slow onset (PGF2
and LVP) would reflect the time needed to cross the cell membrane and activate intracellularly stored calcium ions. Although not specifically studied and quantified in the experiment protocol, it was observed that the duration of the response of vasopressin was longer than that of adrenalin or PGF2
.
It must be emphasized that our ambition was not to perform a full-scale pharmacological analysis of the action of these agents on the peripheral vasculature. Comparisons with other vascular beds were not performed, since the main objective was to compare the local action of the different vasoconstrictors on these vessels with regard to clearly defined clinical problems.
Local injection of PGF2 under laparoscopic control has been shown to be an alternative to surgery in selected cases of ectopic pregnancy (Lindblom et al., 1987
, 1990
; Paulsson et al., 1995
). PGF2
exerts an antigonadotrophic action on the corpus luteum of pregnancy, increases tubal contractility and causes tubal vasoconstriction (Hahlin et al., 1987
). The mechanisms responsible for the therapeutic effect of PGF2
in vivo are, however, far from clear (for reviews, see Lindblom, 1992
, 1994
). Since luteal function and progesterone concentrations are usually markedly depressed in ectopic pregnancy, the antigonadotrophic action of PGF2
is probably of little importance in the majority of cases (Hahlin et al., 1991
). Furthermore, PGF2
and its analogue, 15 methyl PGF2
, have little effect on the viability of cultured human trophoblastic cells (Bengtsson et al., 1995
). Therefore, it seems probable that the main in-vivo effect of PGF2
on ectopic pregnancies is exerted by its vasoconstrictive action on the tuboovarian vasculature and perhaps also by its contracting effect on the tubal muscle. The present study suggests that the addition of LVP or adrenalin to PGF2
could serve two purposes: (i) the vasoconstriction produced would be more powerful that that of PGF2
alone, and the risk of operative and postoperative bleeding would thus be reduced, (ii) the strongerand probably more long-lastingeffect of the drug combination would `trap' PGF2
in the adnexal area and increase the time during which a sufficient concentration of the agent is present in the target tissue.
Another rationale for considering using a combination of two or three compoundseach at a reduced doseis that the risk of systemic side-effects increases with the dose given. The most prominent of the side-effects of LVP are hypertension, bradycardia and pallor. Adrenalin may cause tachycardia and would, in this respect, counteract the effect of LVP. PGF2 may induce coronary arterial constriction but only at high doses accidentally given intravenously. The effect of PGF2
on blood pressure is moderate at the doses used here.
Hyperosmolar glucose has been shown to be at least as effective as PGF2 for local medical treatment of ectopic pregnancy (Lang et al., 1990
). Glucose at high concentrations causes significant inhibition of trophoblast growth in vitro (Bengtsson et al., 1995
) but, according to our recent observations, produces insignificant contractile effects on isolated tuboovarian arteries at equivalent concentrations (B.Lindblom, unpublished data). Accordingly, a combination of several substances, acting on different target tissues, appears to be of great interest for further development of local medical treatment for ectopic pregnancies (cf. Landström et al, 1998
). In addition, the powerful vasoconstriction achieved by combining two or three compounds may be useful in connection with certain other gynaecological operations, e.g. laparoscopic salpingostomy for ectopic pregnancy, treatment of intramural fibroids, haemorrhagic luteal cysts, adnexal adhesiolysis etc.
Theoretically, local injection of vasoconstrictive agents in the adnexal area could induce devastating effects on the ovary with the potential risk of compromising ovarian function acutely or chronically. Although these agents, particularly vasopressin analogues, have been used extensively in gynaecological surgery, there are no indications of such harmful effects. It should be emphasized, however, that to date no studies have addressed this question specifically.
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Acknowledgments |
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Notes |
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References |
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Submitted on October 27, 1997; accepted on September 24, 1998.