Colour-coded duplex sonography of the testes of dogs

Colour-coded duplex sonography was used to examine the testes of 42 dogs whose testes were normal on clinical examination. With colour Doppler, the blood flow in the supratesticular region could be displayed clearly in 70 per cent of the cases, independent of the dog's age, bodyweight, pulse rate and the volume of its testes. The marginal artery could be displayed clearly in 56 per cent of the cases, and the clarity was correlated with bodyweight (P<0.001), testicular volume (P<0.001), and pulse rate (P<0.001). The intratesticular blood flow could not be discerned in 42 per cent of the cases. With pulsed Doppler, the mean resistive index (RI) in the supratesticular region was 0.57, and the mean pulsatility index (PI) was 1.00. In the marginal artery, the mean RI was 0.49, and mean PI was 0.78. In the intratesticular arteries, the mean RI was 0.47, and the mean PI was 0.75. At all three sites both indices were independent of age, bodyweight, pulse rate and testicular volume.

Inhibition of lung phosphodiesterase improves responsiveness to inhaled nitric oxide in isolated-perfused lungs from rats challenged with endotoxin

OBJECTIVES

To investigate the ability of phosphodiesterase (PDE) selective inhibitors to improve responsiveness to inhaled nitric oxide (NO) in isolated-perfused lungs of rats pretreated with endotoxin/lipopolysaccharide (LPS).

DESIGN AND SETTING

Prospective, controlled animal study in the animal research facility of a university hospital.

INTERVENTIONS

Sixteen hours after adult Sprague-Dawley rats were injected intraperitoneally with 0.4 mg/ kg E. coli 0111:B4 LPS administration, lungs were isolated and perfused, and the thromboxane mimetic U46619 was employed to increase the mean pulmonary artery pressure by 5-7 mmHg. The lungs were then ventilated with or without 0.4 ppm NO, and erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA; PDE type 2 inhibitor), milrinone (PDE type 3 inhibitor), or zaprinast (inhibitor of PDE types 5 and 9) were added to the perfusate.

MEASUREMENTS AND RESULTS

In the presence of EHNA (12.5, 25, 50 microM) the vasodilator response to inhaled NO was not greater than in its absence (0.25 +/- 0.25, 0.5 +/- 0.25, 0.75 +/- 0.25 mmHg vs. 0.25 +/- 0.25, 0.5 +/- 0.25, 0.75 +/- 0.25 mmHg, respectively). In the presence of milrinone (125, 250, 500 nM), the vasodilator response to inhaled NO was also not improved. In contrast, zaprinast (3.7, 7.4, 14.8 microM) augmented the pulmonary vasodilatory effect of inhaled NO in lungs from LPS-pretreated rats from 0.25 +/- 0.25, 0.5 +/- 0.25, 0.75 +/- 0.25 mmHg to 0.75 +/- 0.25, 1.5 +/- 0.5, 1.75 +/- 0.75 mmHg, respectively (p < 0.05).

CONCLUSIONS

Our results demonstrate that inhibition of pulmonary PDE enzyme activity with zaprinast increases vasodilator responsiveness to inhaled NO in lungs obtained from rats 16 h after LPS challenge.

Effects of intravenous Zaprinast and inhaled nitric oxide on pulmonary hemodynamics and gas exchange in an ovine model of acute respiratory distress syndrome

BACKGROUND

Inhaled nitric oxide (No) selectively dilates the pulmonary vasculature and improves gas exchange in acute respiratory distress syndrome. Because of the very short half-life of NO, inhaled NO is administered continuously. Intravenous Zaprinast (2-o-propoxyphenyl-8-azapurin-6-one), a cyclic guanosine monophosphate phosphodiesterase inhibitor, increases the efficacy and prolongs the duration of action of inhaled NO in models of acute pulmonary hypertension. Its efficacy in lung injury models is uncertain. The authors hypothesized that the use of intravenous Zaprinast would have similar beneficial effects when used in combination with inhaled NO to improve oxygenation and dilate the pulmonary vasculature in a diffuse model of acute lung injury.

METHODS

The authors studied two groups of sheep with lung injury produced by saline lavage. In the first group, 0, 5, 10, and 20 ppm of inhaled NO were administered in a random order before and after an intravenous Zaprinast infusion (2 mg/kg bolus followed by 0.1 mg. kg-1. min-1). In the second group, inhaled NO was administered at the same concentrations before and after an intravenous infusion of Zaprinast solvent (0.05 m NaOH).

RESULTS

After lavage, inhaled NO decreased pulmonary arterial pressure and resistance with no systemic hemodynamic effects, increased arterial oxygen partial pressure, and decreased venous admixture (all P < 0.05). The intravenous administration of Zaprinast alone decreased pulmonary artery pressure but worsened gas exchange (P < 0.05). Zaprinast infusion abolished the beneficial ability of inhaled NO to improve pulmonary gas exchange and reduce pulmonary artery pressure (P < 0. 05 vs. control).

CONCLUSIONS

This study suggests that nonselective vasodilation induced by intravenously administered Zaprinast at the dose used in our study not only worsens gas exchange, but also abolishes the beneficial effects of inhaled NO.

The use of transmigration and spermac stain to evaluate epididymal cat spermatozoa

Epididymal spermatozoa of domestic cats were diluted with TEST medium and frozen. The parameters - estimated percentage of motile spermatozoa, concentration of spermatozoa, cell morphology and transmigration rate (TMR) - were evaluated before freezing and after thawing. Transmigration is a new method to measure the percentage of spermatozoa that consistently move forward, and has not been investigated with cat spermatozoa until now. Estimated percentage of motile spermatozoa averaged 65%, TMR was 76%, concentration of spermatozoa was 30,000 microl(-1) and the incidence of morphologically abnormal spermatozoa averaged 58% before freezing. After thawing, the estimated number of motile spermatozoa declined by 22%, but TMR remained at 76%. The TMR did not correlate with estimated motility but mostly was higher than the latter, which is postulated to be caused by the mobilizing effect of the countercurrent in the transmigration apparature. The estimated percentage of motile cells in the target chamber of the transmigration apparature was improved by using phosphate-buffered saline (PBS) as transmigration medium. Morphology was assessed both after fixation of spermatozoa in Hancock solution and after staining of smears with Spermac. Spermac did not stain all protoplasmic droplets but proved to be more suitable for the routine examination of acrosomal morphology after thawing.

Randomized, placebo-controlled, blinded and cross-matched study on the antiplatelet effect of inhaled nitric oxide in healthy volunteers

The platelet inhibitory effect of 0-40 ppm inhaled nitric oxide (NO) was investigated in healthy men and women. In both groups, ADP-and collagen-induced platelet aggregation was significantly inhibited 20 (T20) and 40 min (T40) after the beginning of inhalation of 5, 10, and 40 ppm. Moreover, in both men and women, the in vitro bleeding time was significantly prolonged at T20 and T40 during inhalation of 40 ppm. Inhalation of NO also inhibited P-selectin expression at 5, 10, and 40 ppm and fibrinogen binding to the GPIIb/IIIa-receptor at 40 ppm. In conclusion, in healthy volunteers, the platelet inhibitory effect of inhaled NO was not dose-related, since it was significant at 5 and 10 ppm but did not increase during the administration of higher NO concentrations. In addition, gender-related differences were only observed in ADP-induced platelet aggregation at 10 ppm and in bleeding time prolongation at 40 ppm.

Inhibition of nitric oxide synthase prevents hyporesponsiveness to inhaled nitric oxide in lungs from endotoxin-challenged rats

BACKGROUND

Inhalation of nitric oxide (NO) selectively dilates the pulmonary circulation and improves arterial oxygenation in patients with adult respiratory distress syndrome (ARDS). In approximately 60% of patients with septic ARDS, minimal or no response to inhaled NO is observed. Because sepsis is associated with increased NO production by inducible NO synthase (NOS2), the authors investigated whether NOS inhibition alters NO responsiveness in rats exposed to gram-negative lipopolysaccharide (LPS).

METHODS

Sprague-Dawley rats were treated with 0.4 mg/kg Escherichia coli O111:B4 LPS with or without dexamethasone (inhibits NOS2 gene expression; 5 mg/kg), L-NAME (a nonselective NOS inhibitor; 7 mg/kg), or aminoguanidine (selective NOS2 inhibitor; 30 mg/kg). Sixteen hours after LPS treatment, lungs were isolated-perfused; a thromboxane-analog U46619 was added to increase pulmonary artery pressure (PAP) by 5 mmHg, and the pulmonary vasodilator response to inhaled NO was measured.

RESULTS

Ventilation with 0.4, 4, and 40 ppm NO decreased the PAP less than in lungs of LPS-treated rats (0.75+/-0.25, 1.25+/-0.25, 1.75+/-0.25 mmHg) than in lungs of control rats (3+/-0.5, 4.25+/-0.25, 4.5+/-0.25 mmHg; P < 0.01). Dexamethasone treatment preserved pulmonary vascular responsiveness to NO in LPS-treated rats (3.75+/-0.25, 4.5+/-0.25, 4.5+/-0.5 mmHg, respectively; P < 0.01 vs. LPS, alone). Responsiveness to NO in LPS-challenged rats was also preserved by treatment with L-NAME (3.0+/-1.0, 4.0+/-1.0, 4.0+/-0.75 mmHg, respectively; P < 0.05 vs. LPS, alone) or aminoguanidine (1.75+/-0.25, 2.25+/-0.5, 2.75+/-0.5 mmHg, respectively; P < 0.05 vs. LPS, alone). In control rats, treatment with dexamethasone, L-NAME, and aminoguanidine had no effect on inhaled NO responsiveness.

CONCLUSION

These observations demonstrate that LPS-mediated increases in pulmonary NOS2 are involved in decreasing responsiveness to inhaled NO.

Pulmonary vasodilation by nitric oxide gas and prodrug aerosols in acute pulmonary hypertension

Sodium 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA/NO; Et2N-[N(O)NO]Na) is a compound that spontaneously generates nitric oxide (NO). Because of its short half-life (2.1 min), we hypothesized that inhaling DEA/NO aerosol would selectively dilate the pulmonary circulation without decreasing systemic arterial pressure. We compared the pulmonary selectivity of this new NO donor with two other reference drugs: inhaled NO and inhaled sodium nitroprusside (SNP). In seven awake sheep with pulmonary hypertension induced by the infusion of U-46619, we compared the hemodynamic effects of DEA/NO with those of incremental doses of inhaled NO gas. In seven additional awake sheep, we examined the hemodynamic effects of incremental doses of inhaled nitroprusside (i.e., SNP). Inhaled NO gas selectively dilated the pulmonary vasculature. Inhaled DEA/NO produced nonselective vasodilation; both systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) were reduced. Inhaled SNP selectively dilated the pulmonary circulation at low concentrations (< or = 10(-2)M), inducing a decrease of PVR of up to 42% without any significant decrease of SVR(-5%), but nonselectively dilated the systemic circulation at larger doses (> 10(-2)M). In conclusion, despite its short half-life, DEA/NO is not a selective pulmonary vasodilator compared with inhaled NO. Inhaled SNP appears to be selective to the pulmonary circulation at low doses but not at higher levels.

Selective pulmonary vasodilation by intravenous infusion of an ultrashort half-life nucleophile/nitric oxide adduct

BACKGROUND

PROLI/NO (C5H7N3O4Na2 x CH3OH) is an ultrashort-acting nucleophile/NO adduct that generates NO (half-life 2 s at 37 degrees C and pH 7.4). Because of its short half-life, the authors hypothesized that intravenous administration of this compound would selectively dilate the pulmonary vasculature but cause little or no systemic hypotension.

METHODS

In eight awake healthy sheep with pulmonary hypertension induced by 9,11-dideoxy-9alpha,11alpha-methanoepoxy prostaglandin F2alpha, the authors compared PROLI/NO with two reference drugs-inhaled NO, a well-studied selective pulmonary vasodilator, and intravenous sodium nitroprusside (SNP), a nonselective vasodilator. Sheep inhaled 10, 20, 40, and 80 parts per million NO or received intravenous infusions of 0.25, 0.5, 1, 2, and 4 microg x kg-1 x min-1 of SNP or 0.75, 1.5, 3, 6, and 12 microg x kg-1 x min-1 of PROLI/NO. The order of administration of the vasoactive drugs (NO, SNP, PROLI/NO) and their doses were randomized.

RESULTS

Inhaled NO selectively dilated the pulmonary vasculature. Intravenous SNP induced nonselective vasodilation of the systemic and pulmonary circulation. Intravenous PROLI/NO selectively vasodilated the pulmonary circulation at doses up to 6 microg x kg-1 x min-1, which decreased pulmonary vascular resistance by 63% (P < 0.01) from pulmonary hypertensive baseline values without changing systemic vascular resistance. At 12 microg x kg-1 x min-1, PROLI/NO decreased systemic and pulmonary vascular resistance and pressure. Exhaled NO concentrations were higher during PROLI/NO infusion than during SNP infusion (P < 0.01 with all data pooled).

CONCLUSIONS

The results suggest that PROLI/NO could be a useful intravenous drug to vasodilate the pulmonary circulation selectively.

Nitric oxide and sepsis

The ability of NO to control microcirculatory blood flow, maintain vascular integrity, and act as an antiinflammatory mediator appears to be dependent on endothelial-derived NO. The function of excess NO production by iNOS in sepsis and septic shock is unclear but iNOS-derived NO may contribute to systemic hypotension. The use of more specific inhibitors for iNOS will help to define the role of iNOS in sepsis. Modulation of the pulmonary NO-cGMP signal transduction system following LPS treatment results in hyporesponsiveness to inhaled NO and impaired pulmonary vascular response to vasodilators, suggesting potential mechanisms of the pulmonary dysregulation observed in sepsis.

The effect of sperm preparation on the timing of penetration in bovine in vitro fertilization

Five hundred and seventy three follicular bovine cumulus oocyte complexes were matured in vitro and in vitro fertilization (IVF) carried out with the native semen of a brown bull. Half the cultures were fertilized with transmigrated spermatozoa (TM), the other with sperm suspensions prepared using the swim-up (SU) process. Five, six and seven h after IVF the oocytes were fixed and stained. Using a phase-contrast microscope, both the incidence of penetration and polypenetration and the stage of development of a pronucleus were determined. With the TM samples, five hours after IVF penetration was observed in 39.3 per cent of the oocytes, whereas with the SU samples the first instances of penetration were observed only two hours later (4.2%). By this time a normal-looking pronucleus was observed in 16.4 per cent of the oocytes in the TM group. Polypenetration was seen only after seven hours of incubation. This study showed that TM spermatozoa penetrate the oocyte earlier than SU spermatozoa.

[Effect of quality markers of ejaculates of beagle dogs after frequent semen collection]

Semen was collected from 4 adult beagle-dogs twice weekly during six months. The libido did not alter and frequent semen collection did not deteriorate the investigated parameters. Because of a bad constitution, the semen quality of one male was not sufficient. The mean volume of the second fraction of the remainder slightly decreased from January until June from 1.2 to 0.5 ml. On the contrary the mean volume of the first and third fraction increased, mainly from April until May from 0.3 to 1.0 (first fraction) and from 1.0 ml to 5.0 ml (third fraction), resp. The average of the sperm number/microliter augmented from month to month from 71.3 to 324.4 x 10(3)/microliter. The transmigration rate reached its maximum in April (52.2%). The monthly average number of the percentage of morphologically abnormal spermatozoa correlated with the corresponding transmigration rate. There were negative, linear relationships between specific morphological abnormalities of spermatozoa and both estimated motility and transmigration rate.

Hyporesponsiveness to inhaled nitric oxide in isolated, perfused lungs from endotoxin-challenged rats

Inhaled nitric oxide (iNO) causes selective pulmonary vasodilation and improves oxygenation in patients with the adult respiratory distress syndrome (ARDS). Approximately 30% of ARDS patients fail to respond to iNO. Because sepsis syndrome often accompanies a decreased response to iNO, we investigated NO responsiveness in isolated, perfused lungs from rats exposed to lipopolysaccharide (LPS). Eighteen hours after intraperitoneal injection of 0.5 mg/kg LPS, rat lungs were isolated, perfused, and preconstricted with U-46619. Ventilation with 0.4, 4, and 40 parts per million by volume NO vasodilated LPS-pretreated lungs 75, 47, and 42% less than control lungs (P < 0.01 value differs at each concentration). The diminished vasodilatory response to iNO was associated with decreased NO-stimulated guanosine 3',5'-cyclic monophosphate (cGMP) release into the perfusate. Soluble guanylate cyclase activity did not differ in lung extracts from LPS-pretreated and control rats. LPS increased pulmonary cGMP-phosphodiesterase (PDE) activity by 40%. The PDE-sensitive cGMP analogue 8-bromoguanosine 3',5'-cyclic monophosphate vasodilated lungs from LPS-pretreated rats less than lungs from control rats. In contrast, the PDE-insensitive 8-para-chlorophenylthioguanosine 3',5'-cyclic monophosphate vasodilated lungs equally from both groups. After LPS challenge, the rat pulmonary vasculature becomes hyporesponsive to iNO. Hyporesponsiveness to iNO appears partly attributable to increased pulmonary cGMP-PDE activity.

[Modification of the quality indicators of the ejaculate of beagle dogs due to frequent collections over time]

Ejaculates from five adult beagle dogs were investigated for changes of spermatologic parameters. Semen was collected daily during 12 weeks. The parameters volume, sperm count, and transmigration rate (TMR) increased during the first three to five weeks and decreased in the middle of the experiment. The percentage of morphologically abnormal spermatozoa just exceeded 20% from the fifth to the seventh week and in the tenth week, respectively. Either the results remained on a low level (volume), or they returned to normal from the tenth week on (morphology, TMR, sperm count). Semen quality diminished after five weeks. It is concluded, that daily semen collections during more than five weeks can cause decreased libido, aspermia, and impairment of the conception rates.

In vivo lipopolysaccharide pretreatment inhibits cGMP release from the isolated-perfused rat lung

Administration of bacterial lipopolysaccharide (LPS) to rats stimulates synthesis of nitric oxide (NO), a free radical molecule that activates soluble guanylate cyclase, thereby increasing intracellular guanosine 3',5'-cyclic monophosphate (cGMP) concentration and inducing systemic vasodilatation. To investigate the effect of endotoxemia on the pulmonary NO/cGMP signal transduction system, we measured the release of cGMP by isolated-perfused lungs of rats that received an intraperitoneal injection of LPS (1 mg/kg) or saline 2 days earlier. Over 90 min, 1.4 +/- 0.78 and 0.079 +/- 0.016 nmol cGMP accumulated in pulmonary perfusates of saline- and LPS-treated rats, respectively (P < 0.05). Despite addition to the perfusate of Zaprinast, superoxide dismutase, or A23187, markedly less cGMP was released from the lungs of rats exposed to LPS than from the lungs of control rats. In contrast, after ventilation with 100 parts per million NO gas, cGMP accumulating in the perfusate of the lungs of both groups of rats was markedly increased, and the quantity of cGMP released from the lungs of LPS-treated rats was similar to that released by control rat lungs (2.8 +/- 0.57 vs. 3.3 +/- 0.88 nmol, P = NS). With the use of immunoblot techniques, equal concentrations of constitutive endothelial NO synthase were detected in the lungs of rats treated with saline or LPS. These results demonstrate that the NO/cGMP signal transduction system is abnormal in the lungs of rats exposed to LPS, at least in part, at the level of endothelial NO synthase activation.

Propofol-induced alterations in the microcirculation of hamster striated muscle

To investigate the effects of propofol on small vessels, we have measured changes in diameter and blood flow in microcirculatory venules and arterioles. Studies were carried out in the dorsal skinfold chamber of hamsters by intravital fluorescence microscopy. A bolus injection of propofol 25 mg kg-1 dilated small and collecting venules by a mean value of 18% and arterioles by 13%. Blood flow in venules increased by up to 69%. Intralipid dilated arterioles and post-capillary venules by 26% and 30%, respectively. After 4 h of continuous infusion (0.2-0.8 mg kg-1), only blood flow in post-capillary venules increased (66% propofol and 92% Intralipid). Post-capillary and collecting venules dilated in both groups. Therefore, propofol and Intralipid induced venodilatation and enhanced blood flow after bolus administration. After 4 h, despite dilatation in both groups, only post-capillary venules showed enhanced blood flow. These observations suggest redistribution of blood flow after prolonged administration of propofol.

[The influence of semen preparation and culture medium on the success of IVF in cattle]

The effect of two semen-preparation methods and the presence and absence of capacitation-inducing supplements in the fertilization medium on IVF-results were examined in a 2 x 2 factorial design. In vitro matured oocytes were fertilized either with transmigrated (TM) or with swim-up (SU) prepared native semen. In the first group, the fertilization medium contained 0.8 microgram/ml heparin, 1.2 micrograms/ml hypotaurine and 0.2 microgram/ml epinephrine. However, in the second group, no capacitation-inducing or motility-enhancing substances were used. After SU-treatment, the supplements were necessary to obtain sufficient fertilization results. In the second group (non-supplemented medium), the percentages of penetrated and fertilized oocytes were decreased significantly (P < 0.001). By contrast, transmigrated semen required no additional supplementation of the fertilization medium. The penetration and fertilization rates of this semen-preparation method were equal in both groups.

[The use of rapid progesterone tests (Serozyme-Progesterone, Ovucheck) for the diagnosis of pregnancy in Austrian mountain sheep]

To determine the oestrous cycle length of mountain sheep 10 ewes were stimulated with intravaginal sponges (Chronogest) and ten with prostaglandins (Iliren) and a PMSG injection (500 IU), respectively. Independent of the synchronisation mode the Serozyme-progesterone levels indicated a cycle length of 17 days. Progesterone was not detectable by the test system during oestrous, it reached its maximum on the 10th day (mean = 3.9/3.7 ng/ml) and decreased to non-detectable levels again on day 17. For early pregnancy diagnosis the Serozyme-progesterone as well as the Ovucheck gave useful results. On day 17 and 19 after mating the progesterone concentration of pregnant ewes remained on the same level as on day 10, whereas barren ewes had non-detectable progesterone levels on day 17 and 19, using the Serozyme-progesterone and below 1 ng/ml on day 19 using the Ovucheck. The accuracy of the Serozyme-progesterone referring to the declaration "non pregnant" was 100%, that of the Ovucheck 37.5% on day 17 and 100% on day 19. The use of both test systems for determining pregnancy of unknown length was examined by collecting blood-samples three times with a five and a seven day interval. Precise results were obtained only with the Serozyme-progesterone test. At least one of three blood samples of all the barren ewes (n = 8) contained amounts of progesterone beneath the sensitivity of this method. The Ovucheck results could not help at all to distinguish barren or pregnant ewes with unknown mating data.

[Indirect detection of ovulation and fertilization in the dog by progesterone level testing]

In addition to already published data (Arbeiter et al., 1990) we could achieve important facts concerning the estimation of mating time of the bitch by measuring the progesterone (P4) level continuously and observing the clinical signs on a collective of 106 ambulant patients. We found that a P4-concentration of 5 ng/ml plasma and above is signaling ovulation or ova fertilisation; a sudden rise of the progesterone over 10 ng (Ovucheck), reflecting 19.2 ng/ml (Serozyme-Progesterone), turned out to be a diagnostic mark for determination of mating time. Copulation took place between the 9th and 19th day of heat. 89% of the controllable bitches (n = 79) conceive and birth occurred 61.4 days (mean) later. The litter size and the loss of dead born puppies (4.7%) was normal with regard to the pertinent races. Because of their easy handling the P4-test kits (Ovucheck; Serozyme-Progesterone) are of good use for the practitioner.

Intracavernous injection of vasoactive drugs in the rabbit

To investigate the erectile response and side effects of intracavernous injection of vasoactive agents, 7 groups of 5 rabbits each underwent injection of either isotonic saline or 1 of 6 drugs. Phentolamine most consistently produced full erection with few inflammatory reactions, while phenoxybenzamine produced erection but also severe inflammation and sclerosis of the corpus cavernosum. With prostaglandin E1, neither erection nor inflammation was observed.

Tiamulin, a new antibiotic for eliminating mycoplasmas from bovine serum

Tiamulin, a new diterpene antibiotic, was investigated for toxicity to spermatozoa. The compound was added to ejaculates via semen extender at a concentration of 50 to 90 mg per 100 ml of total liquid. Motility and the proportion of non-viable spermatozoa were used as criteria of the drug's effect. Tiamulin proved to be safe up to doses of 70 mg per 100 ml of semen extender.

[Prerequisites for enhancement of the efficacy of fosfomycin by glucose-6-phosphate in treatment of experimentally infected animals (author's transl)]

In chemotherapy of otherwise fatally infected mice (intraperitoneally) the effective dose50 (ED50) of fosfomycin (2 single doses, subcutaneous application 1 and 6 h post infect.) was decreased significantly by supplementing the antibiotic solution with 100 mg glucose-6-phosphate (G-6-P) per kg animal and per injection if also the MIC of the infecting strain (Klebsiella oxytoca and K. aerogenes II) was lowered by addition of G-6-P (25 mg/l) to the nutrient medium (Table 1 and 2). With strains not exhibiting any influence on the MIC no such effect was observed (Table 1). From this it is concluded that the enhancement of antimicrobial activity of fosfomycin in vivo is based on the same mechanism as in vitro. This mechanism is the initiation of a second route of transportation into the bacterial cell (7), the hexose-6-phosphate transport system that apparently is inducible not only in vitro but also in vivo. Blood levels of G-6-P sufficient or above to induce this system in vitro (5 mg/l) were being held with doses of 100 mg/kg body weight in dogs during 70 to 120 min (Fig. 3) and 45 to 70 min (Fig. 4) when applied subcutaneously or intravenously respectively. These periods of contact area adequate to induce a considerable decrease of the MIC. With the strain used (K. oxytoca) the MIC of 128 mg/l was lowered by contact with G-6-P during 60 or 120 min to 16 or 8 mg/l respectively (Fig. 5). For full induction of the hexose-6-phosphate system resulting in a MIC of 2 mg/l however, 8 h were necessary. From the above findings it is concluded that clinical studies are necessary. As G-6-P is a (short-lived) physiological product of cell metabolism and nontoxic such studies are justifiable in cases where therapeutic use of fosfomycin can be regarded as an indication.